feat(docs): Updated container info

[r0ssing]

Changes

• docs/guides/deployment.md

  • Replaced the outdated image-tag table with the deployment-oriented overview.
  • Documented latest, latest-pre-release, dev, main, versioned tags, and sha-*.
  • Clarified that dev is not the published pre-release channel.
  • Explained when release pointer tags move.
  • Added a Watchtower example using:

    image: ghcr.io/opendataensemble/synkronus:latest-pre-release

  • Clarified mutable versus fixed tags and recommended pinned versions for production.

• docs/development/building-testing.md

  • Corrected the GitHub Actions triggers and generated tags.
  • Removed stale feature-branch publication guidance.
  • Linked to the deployment guide.

• docs/reference/synkronus-server.md

  • Added a pointer to the deployment guide’s image-channel documentation.