Automate post-release steps

[marcphilipp]

• Add job for releasing the staging repository
• Add job for publishing documentation
• Add job for closing the GitHub milestone of the release
• Add job for waiting for sync to Maven Central
• Add job for updating samples after sync to Maven Central was successful
• Add job for creating a GitHub release

New workflow

        ╭───────────────────────────────────╮ ╭─────────────────────────────────╮
        │ Verify artifacts are reproducible │ │ Verify artifacts are consumable │
        ╰───────────────────────────────────╯ ╰─────────────────────────────────╯
                                           ⬇
                             ╭────────────────────────────╮
                             │ Release staging repository │
                             ╰────────────────────────────╯
                                           ⬇
 ╭────────────────────────────────╮ ╭───────────────────────╮ ╭────────────────────────╮
 │ Wait for sync to Maven Central │ │ Publish documentation │ │ Close GitHub milestone │
 ╰────────────────────────────────╯ ╰───────────────────────╯ ╰────────────────────────╯
                                           ⬇
                      ╭────────────────╮ ╭───────────────────────╮
                      │ Update samples │ │ Create GitHub release │
                      ╰────────────────╯ ╰───────────────────────╯