Merge remote-tracking branch 'origin/NR_UE_prevent_unnecessary_assertions' into integration_2024_w26b

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Integration: `2024.w26`

See merge request oai/openairinterface5g!2815

* !2750 Add Ubuntu 24.04 to/retire Ubuntu 18.04 from supported distributions, use Ubuntu 22 for CI container images
* !2793 Option '-O' in phy simulators to provide a configuration file
* !2797 Increase TX_DATA.request TB buffer size, fix compute_PDU_Length
* !2814 Update documentation and FEATURE SET
* !2720 Remove thread-pool Makefile
* remove extra log

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

Fixed delta MPR.
Fixed an error in PUCCH PC_MAX calculation.

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+.