bypass acceptance tests for release notes

[domdom82]

• With the addition of acceptance tests, the build time got bumped significantly higher. (> 20m)
• Acceptance tests are expensive and only make sense if there are changes to test.
• To make a new release, we need to add release_notes.md
• CI should skip acceptance tests if the PR contains only release_notes.md (maybe also README.md changes)
• CI should still run tests if the PR contains other code

[peanball]

We could add [no-ci] or some similar text to release note commits, which would not run the CI task, or rather run an abbreviated task that skips CI and marks the step successful.

[plowin]

I think rel-notes are often part of a PR including a feature.
As label is on a PR, we probably rather need to adjust it on a code-level

[peanball]

Please consider any file changes that don't affect the acceptance tests as "to be ignored". This includes the pipeline definition and support scripts for the pipeline (e.g. shipit)