Document new pipeline changes

[Ekhorn]

Description

It would be nice to have a page I can refer to that mentions the new CI/CD pipeline concepts introduced in openremote/openremote#2696

Acceptance criteria

• How to make changes to the pipeline and test them
• "environment" and "job" workflows are documented
• What to include in artifacts and when to use artifacts
• When to configure through Gradle rather than workflows
• Good/bad practices
  • Add timeout-minutes: 20 to any step that could fail and hang
  • Avoid passing toJSON(secrets) whenever possible (never pass secrets this way to another workflow), either explicitly pass secrets using secrets: { MY_SECRET: ${{secret.MY_SECRET}} } (preferred) or use secrets: inherit.
• How we optimize jobs and job dependencies
  • When to checkout with git lfs
  • The detect changes job
  • Only installing the bare minimum dependencies in jobs e.g. with yarn focus @openremote/util @openremote/test
  • Tricks like updating file modified metadata to make build tooling use artifact outputs (after downloading them)
• How deployments work
• Refer to specific GitHub concepts
  • Mention how to write and update composite actions
  • How the reusable workflows work
    • Like why we need to handle skipping inside the reusable workflows
  • Maybe some special conditions e.g. when an always() is used (often used for test results etc.)
• Caching strategies? e.g. docker images