feat: add ocis_helper

[mmattel]

The ocis helpers, an essential component to automate the generation of envvar docs, originally lived in the ocis repo, created many years ago, were never manintained and finally became inactive when changing to ocis 8.0

This PR:

• Migrates the helpers by a decision with @kobergj and @mmattel to the docs side which eliminates a lot of task dependencies
• Updates the helpers massively and bring them to a new level.
• Migrate and integrate the delta file creation (added, deprecated and removed envvars) to go, originally a Python script.
• Add new functionalities to helpers, especially with the -d flag which highlights for envvars inconsistent defaults or inconsistent descriptions.
• Add a README
• For all ocis releases:
  • Add required persistent files per version
  • Copied generated files per version for the Antora build process

Note that this PR DOES NOT add the required doc build changes to access the files generated. This will come in an additional PR.

When this PR is merged, we can cleanup the docs folder in the ocis repo.