[CI] Skip SemVer on R0-silent and update docs (#6285)

Changes:
- Make R0-silent not run the semver check again. Originally I thought
this would be good to have a bullet-proof check, but it now often
triggers when CI or unrelated files are changed. In the end, the
developer has to make the right choice here - and always will need to.
So bringing back the R0 label gives more power to the devs and should
increase dev velocity. We still need to ensure that every use of this
label is well understood, and not just used out of lazyness.
- Fix `/cmd prdoc` bump levels
- Update docs

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Signed-off-by: Oliver Tale-Yazdi <[email protected]>