chore: introduce Stalebot

[anakin87]

In Haystack repo, we have a similar Stalebot: if an issue is tagged with community-triage, it is tagged as stale after 30 days with no activity, then closed after 10 additional days.

Proposed Changes:

Introduce a Stalebot workflow for core-integrations

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.