TASK: Documentation tweaks, add CR command reference

[kdambekalns]

• This does some cleanup and improvements to the documentation.
• Tweaks documentation-related settings.
• Slightly cleans up some code (CR commands)

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[bwaidelich]

This is fantastic, thank you.
I only skimmed over the changes and could not find any obvious error, so +1 by reading.

We should merge this asap to prevent conflicts

[kdambekalns]

Anyone up for a second approval, so I can merge this?

[dlubitz]

Looks good, I just wonder why you've removed all ChangeLogs and ReleasNotes?

[kitsunet]

Technically they were never supposed to be in there, but over the years we collected them due to upmerges. Original idea was to have only tthe ones for the current branch, so 8.1 branch contains all but only the 81x notes.

[kdambekalns]

And the result: https://neos.readthedocs.io/en/9.0/References/ContentRepositoryCommandReference.html