"Post job cleanup" output should be collapsed by default

Description

Problem: The post job cleanup enabled with FF_ENABLE_JOB_CLEANUP feature flag pollutes the job log and makes it more difficult to find the actual root cause of a job failure.

What it currently looks like:

Cleaning up project directory and file based variables
00:01
Removing context/
... # Lots of lines here
Removing docker_image_build.env
HEAD is now at 83b95b8e fix/blablabla
Job succeeded

Proposal

Pre-collapse the section Cleaning up project directory and file based variables with [collapsed=true]. The user can expand it if necessary, but the output of cleanup hardly ever matters.

Links to related issues and merge requests / references

The current implementation: !3065 (merged)