chore(ci): migrating flexric test to carabe

Preparing the Jenkins server migration: Phase 1 --> decorrelating the CN5G CI resources from the RAN resources

I put in documentation since we don't need to run CI on it.

I've run manually on carabe and it is passing.

parameters for OAI-FLEXRIC-RAN-Integration-Test pipeline have to be changed as well from selfix to carabe.

2 other pipelines have to be reconfigured:

• RAN-ARM-Cross-Compile-Builder
• RAN-cppcheck

Both will be running on carabe as well for the moment.

TODO:

• create a carabe agent in old jenkins instance.
• make a dummy jenkins file for OAI-CN5G-COTS-UE-Test pipeline that generates an empty HTML file