This reverts a change in commit
ccba7c87. There is no real reason to
show this warning (the gNB will work just fine, simply not schedule
since no free HARQ) and it makes users unsure.

Extract thread-pool into a separate CMake library.
Extract utils into a separate CMake library.

- come straight to point: how to clone (don't talk about git config)
- refer to contributing documentation where necessary instead of
  repeating information

- CellGroupConfig is handled through DU (hence MAC)
- mention number of DUs/CU-UPs handled per CU-CP
- mention number of UEs handled
- take out BWPs, as we don't support it properly
- typos

Update instructions and CI for cross-compilation on Ubuntu 22.
Note that for the dockerfile, we use egrep -L which has changed and does
not exit with code 0 on no match. Instead, use -vqz to invert return
code (0 if nothing found, otherwise 1).

iperf2 2.0.13, used in Ubuntu 20, does not need a "back channel"; we can
therefore use it in feMBMS (which does a broadcast, without back
channel). Ubuntu 22 comes with 2.1.5, which seems to require a back
channel, or at least, we cannot use it reliably in feMBMS. Hence,
downgrade to older iperf2 version.
Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

This updates all images in the CI to Ubuntu 22. It also updates
corresponding documentation. Remove python(2) from the image, as it is
not needed. Update documentation.

It seems that the gcc coming in Ubuntu 22 does not like
stack-protector-strong, so remove it as well.

Since we compile Flexric, which does not support Ubuntu 22's default
gcc-11 (it hits a compile bug), switch to gcc-12 manually.

Since we update the compiler, we also need to be careful to use the right
address sanitizer version (which is bundled with the compiler version).
To avoid a reinstallation of the wrong asan version in target images, we
modify Ubuntu 22 targets to copy libasan from the base image. This is necessary
since we use update-alternative in the base image, but we don't want to
install compilers in the target images to use update-alternatives to
install the right asan version... This should be undone when switching
to Ubuntu 24 in the future, as it will have a newer default gcc version,
such that we don't need to update the compile in the first place.

Upgrade libpython in lteUE for U22 upgrade to make it compatible with
UHD.

A number of warnings appear when compiling flexric with gcc-12, which we
use in the next commit. Those have been fixed upstream. Switch to the
updated version to avoid warnings.

It seems libatlas-base-dev provided an `enum CBLAS_TRANSPOSE`, but we
don't install it anymore. Now, in Ubuntu, there is only a typedef'd
version in cblas.h; for RHEL(-derivatives), the same typedef'd version
is in cblas/cblas.h.

Debian 11: cmake 3.18
Fedora 40: cmake 3.29
RHEL 9: installs cmake3, which is typically very recent, likely 3.29
Ubuntu 20: cmake 3.16

Ubuntu 18.04 is now in "Extended Security Maintenance", but otherwise
gets no updates. Remove it from supported distributions (regarding
installing packages); users can of course still use it.

Users are encouraged to upgrade to Ubuntu 20+.

Apart from the obvious change of adding ubuntu24.04 to supported
distributions, we need to remove liblapacke-dev as it is incompatible
with libatlas3-base. Installing both aborts with:

   The following packages have unmet dependencies:
   liblapacke : Breaks: libatlas3-base (< 3.10.3-14) but 3.10.3-13ubuntu1 is to be installed

It seems that we don't need it though, as liblapacke-dev installs the
right atlas library as a dependency.

Change TX_DATA.request PDU_Length and TLV length parameters to 32 bit in related pack/unpack procedures.
Fix small issue noted when packing tlv value with tag 1 in which it would pack length*4 bytes, now calculated how many "segments" of 32 bits it needs to pack, same logic for unpacking tag value 1

Increase TX_DATA.request TB buffer size to be allocated in the stack with 2MB, fix compute_PDU_Length to not truncate value and fix packing procedure to use buffer size as the upper limit instead of hardcoded value

Integration: `2024.w25`

See merge request oai/openairinterface5g!2811

* !2795 NR UE NL assertion
* !2802 Fix regression in ue-scan-carrier option
* !2806 Minor fixes to wireshark documentation
* !2807 Add assertion for known segfault during teardown of gNB
* !2809 Inversion in flags name
* !2697 SIDELINK PSBCH: MAC->PHY cfg, Scheduler + supporting functions, enable system testing & scope
* !2808 NR UE DLSCH MCS table selection improvements

fix(phy_simulators): enable the use of option -O to pass a configuration file to configmodule in phy simulators

	- Phy config update and Sidelink frame parameters initialisation
	- PSBCH scheduler to trigger TX PSBCH/RX PSBCH actions
	- Sidelink indication with rx ind to trigger send SL-MIB to MAC
	- Enable Scope for PSBCH use -d or --dqt
	- Enable system testing of PSBCH for example using RFSIMULATOR:

		- UE1 is a SYNCRONISATION SOURCE UE which transmits PSBCH

		  started using command -
		  sudo ./nr-uesoftmodem --sl-mode 2 --sync-ref 4 --rfsim --rfsimulator.serveraddr server

		- UE2 syncs onto UE1 during sidelink search, gets the timing and continues to receive PSBCH

		  started using command -
		  sudo ./nr-uesoftmodem --sl-mode 2 --rfsim --rfsimulator.serveraddr 127.0.0.1

		- In the default use case 2 Sidelink SSBs sent over 16 frames.

		- In case SL-SSB configuration needs to be changed use -O option in the above command like

		-O ../../../targets/PROJECTS/NR-SIDELINK/CONF/sidelink_preconfig_1txpool.conf

Integration: `2024.w24`

See merge request oai/openairinterface5g!2801

* !2789 CI: Increase iperf/iperf3 command timeout
* !2762 improve nrUE NAS security: accept NEA1,NEA2,NIA1,NIA2
* !2791 fix regressions for large physical cell id values
* !2792 Add support for MIMO 2x2 with USRP B210 at 20 MHz BW and 3/4 sampling rate
* !2748 Small UE fixes
* !2745 Add google test testcases for nr_get_Pcmax
* !2785 Update FHI 7.2 interface, test bandwidths, fix integer overflows