Add CI to enforce version bumps in pull requests

[Copilot]

The repository follows a "live at head" approach where every merge to master triggers a release. This requires strict version discipline but lacked enforcement.

Changes

Version check workflow (.github/workflows/version-check.yml)

• Runs on PRs targeting master
• Compares diracx/Chart.yaml version against base branch
• Fails if version unchanged
• Scopes to top-level charts only (subcharts not released independently)
• Minimal permissions: contents: read

Contributing guide (CONTRIBUTING.md)

• Version bump requirement and semantic versioning guidance
• "Live at head" workflow explanation
• Recommended branch protection settings (require up-to-date branches, linear history)

Repository configuration guide (docs/REPOSITORY_CONFIGURATION.md)

• Branch protection rule configuration for administrators
• Required status checks: pre-commit, run-demo, run-demo-mount-sources, check-version-bump
• Rationale for enforcing up-to-date branches and linear history

Example

A PR without a version bump will fail:

❌ ERROR: Version in ./diracx/Chart.yaml has not been bumped!
   Current: 1.0.0
   Base: 1.0.0
   Please increment the version in ./diracx/Chart.yaml

Bumping from 1.0.0 to 1.0.1 passes the check.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add CI to ensure the version is always bumped in MRs</issue_title>
<issue_description>I think we'll need a "live at head" approach for the charts repo and separate development branches.

This is because the repo is pushed to by diracx and diracx-web so it'll always tag the main branch.

We should also require that PRs are up to date before merging (and maybe a linear history).</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add CI to ensure the version is always bumped in MRs #173

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