docs: add Forgejo as integration

[Ryuno-Ki]

📑 Summary

Added Forgejo as integration

Resolves N/A (as Add to Mermaid Ecosystem indicated to open a PR directly -- but then Update Documentation is slightly contradicting it here)

📏 Design Decisions

As a (by now hard) fork of Gitea Forgejo has also inherited Mermaid support. (Including security updates when needed)

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests. ➡️ N/A
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features. ➡️ is there something I need to edit also?
• 🦋 If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:. ➡️ I went with docs.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e70b069

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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commit: e70b069

[Ryuno-Ki]

Changed files were transformed in src/docs but do not match the files in ../../docs. Please run 'pnpm --filter mermaid run docs:build' after making changes to src/docs to update the ../../docs directory with the transformed files.

Looks like you're not set up to accept changes using GitHub's web editor, huh?

I'll run the command if you have taken a look at the change itself if you want me to.