Update some links after repository migration

[clange]

• from dev meeting invite to meeting minutes (Wiki)
• relative links between wiki pages (Markdown syntax differences)
• meeting minutes: in the minutes until 2025-05-08, rewrite links like #123 to issue/MR URLs in the old GitLab
  • @moosmannp to ask whether old repo will remain archived for a long time (to serve as documentation)

[SchulzeStTSI]

@clange Repo remains archived. But if you miss any content feel free to move it to GitHub (Comments from old discussions for instance were not migrated, they should be renewed here)