[Feat] Move maintanance scripts to a separate infrastructure repo

[wenzeslaus]

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Is your feature request related to a problem? Please describe.

The grass-addons repo contains infrastructure scripts relevant to the core repository which are not addons, so that's confusing.

Additionally, the primary group contributors with write access to the grass-addons repo is different group than the maintainers of the infrastructure scripts which are also in the grass-addons repo.

Describe the solution you'd like

A separate repository seems best.

Describe alternatives you've considered

Neither core nor addons repo are good matches for scripts for a specific server. However, documentation could be build in GitHub Actions based on every commit on the given branch and uploaded to a publishing server. In that case, both core and addons is the appropriate each for its respective documentation/artifact scripts.