Merge remote-tracking branch 'origin/cleanup-build-oai-speedup-cluster' into integration_2025_w33 (!3579)

CI: speed up and simplify build, remove unnecessary Python code, remove --eNB* parameter list

This cleans up the CI framework for running end-to-end tests, and
improves the integration with OAI code. Specifically

- cleanup build_oai and helpers to output all text, which is captured
  better by the CI
- build some images in the Cluster-Build in parallel to increase speed
- remove all --eNB{,1,2}{IPAddress,UserName,Password} variables. Those
  were indexed through "instance" and "server ID" and are replaced with
  the actual node name. I consider further cleanup to introduce a
  "global" XML file node name so we don't need this in each step and
  instead define this once.
- individual cleanup

doc/README.md

@@ -133,6 +133,8 @@ The other SDRs (AW2S, LimeSDR, ...) have no READMEs.
 - Component tests are under `tests/`. Currently, there is a simple CU-UP
   tester, see the corresponding [README.md](../tests/nr-cuup/README.md).
 - [TESTBenches.md](./TESTBenches.md) lists the CI setup and links to pipelines
+- The CI setup uses a [custom framework](../ci-scripts/README.md) to run
+  end-to-end tests.
 
 # Developer tools