Remove cppcheck from CI, add to tools/

We don't enforce cppcheck through the CI, although it's there since
years. It runs on Ubuntu 18/20, so it's old. For folks, it's likely not
discoverable on how to run it locally. Let's make a fresh start.

This removes cppcheck from all CI-related code. Instead, it adds it
under tools/cppcheck/, including documentation on how to run it locally,
bare-matel or in docker.

Signed-off-by: Robert Schmidt <robert.schmidt@openairinterface.org>

doc/TESTBenches.md

@@ -96,10 +96,6 @@ information on how the images are built.
   - orion: Cross-compilation from Intel to ARM
   - base image from `Dockerfile.base.ubuntu.cross-arm64`
   - build image from `Dockerfile.build.ubuntu.cross-arm64` (no target images)
-- [RAN-cppcheck](https://jenkins-oai.eurecom.fr/job/RAN-cppcheck/)
-  ~BUILD-ONLY ~4G-LTE ~5G-NR ~nrUE
-  - bellatrix
-  - performs static code analysis, currently not actively enforced
 - [RAN-RHEL8-Cluster-Image-Builder](https://jenkins-oai.eurecom.fr/job/RAN-RHEL8-Cluster-Image-Builder/)
   ~BUILD-ONLY ~4G-LTE ~5G-NR ~nrUE
   - cluster (`Asterix-OC-oaicicd-session` resource): RHEL image build using the OpenShift Cluster (using gcc/clang)