[Buildbot] Add Buildbot build status badge

[LuxologyGG]

Closes #6837

Summary

Adds a new Buildbot build status badge that queries a self-hosted Buildbot instance's REST API for the latest build result on a given builder.

Example

https://img.shields.io/buildbot/build/amd64-rhel8-dockerlibrary?baseUrl=https://buildbot.mariadb.org

Changes

• Add services/buildbot/buildbot.service.js — fetches {baseUrl}/api/v2/builders/{builder}/builds?limit=1&order=-number and maps Buildbot result codes to badge status
• Add services/buildbot/buildbot.service.spec.js — unit tests for URL building, result transformation, and rendering
• Add services/buildbot/buildbot.tester.js — live and mocked integration tests

API rate limits

The Buildbot REST API documentation does not define request rate limits. Buildbot is self-hosted, so any throttling is configured by the operator (for example via a reverse proxy). This badge issues a single GET per request with limit=1.

Review feedback addressed

• Fixed ESLint failures (no-unused-vars, sort-class-members, Prettier)
• Rebased onto current master
• Documented API rate-limit behavior in the service description and this PR body

Checklist

• Service implementation (services/buildbot/buildbot.service.js)
• Unit tests (services/buildbot/buildbot.service.spec.js)
• Service tests (services/buildbot/buildbot.tester.js)
• npm run test:core -- --grep Buildbot (15 passing)
• npm run test:services -- --grep Buildbot (3 passing)
• npm run lint (0 errors)

[github-actions]

	Messages
📖	✨ Thanks for your contribution to Shields, @LuxologyGG!

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[PyvesB]

Hello @LuxologyGG 👋🏻 What are the API rate limits?

[LuxologyGG]

Hello @LuxologyGG 👋🏻 What are the API rate limits?

Same answer, the Buildbot REST API rate limits depend on the self-hosted instance. Since this targets user-hosted servers, there's no universal limit. Happy to add a note in the docs about it

[LuxologyGG]

The Buildbot REST API documentation does not document request rate limits. Buildbot is self-hosted, so any throttling is configured by the operator (for example via a reverse proxy in front of the web server; see the Web Server configuration docs).

This badge issues one GET request per badge render to {baseUrl}/api/v2/builders/{builder}/builds?limit=1&order=-number. I have documented this in the service description and updated the PR body accordingly.

I have also fixed the ESLint failures (no-unused-vars, sort-class-members, Prettier) and rebased onto current master.