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>

tools/cppcheck/docker-compose.yaml

@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: MIT
+
+services:
+  cppcheck:
+    image: cppcheck
+    build:
+      dockerfile_inline: |
+        FROM ubuntu:focal
+        RUN DEBIAN_FRONTEND=noninteractive apt update && apt install -y cppcheck
+    volumes:
+      - ../../:/code/
+    command:
+      bash -c "cd /code/ && ./tools/cppcheck/run-cppcheck.sh"
+