Add Copilot skill for Azure.Provisioning library regeneration

[ArcturusZhang]

Description

Add a new Copilot skill document that guides the process of regenerating Azure.Provisioning.* libraries to add new resources or features.

Use Cases

This skill is useful when:

• New resource types need to be added to provisioning (e.g., NetworkSecurityPerimeter)
• New enum values are added (e.g., new PostgreSQL server versions)
• New API versions bring new properties or types
• The management library has a new release with features needed in provisioning

Skill Workflow

The skill covers the complete workflow:

1. Determine if management library version update is needed
2. Update version in eng/Packages.Data.props (if needed)
3. Check for resource whitelist in specification files (if applicable)
4. Run the provisioning generator with --filter {ServiceName}
5. Verify only target library changed (revert unintended changes)
6. Validate generated schema against Azure Bicep reference documentation
7. Handle breaking changes with backward-compatible customizations
8. Fix spell check issues in sdk/provisioning/cspell.yaml
9. Export API and update snippets
10. Run pre-commit checks
11. Update CHANGELOG and commit

Key Files

File	Purpose
.github/skills/provisioning-library-regeneration/SKILL.md	The skill document

Testing

This skill was developed and validated while fixing:

• #55583 - PostgreSQL versions 17 and 18
• #56426 - NetworkSecurityPerimeter resources

[Copilot]

Pull request overview

Adds a new GitHub Copilot skill document to standardize the workflow for regenerating Azure.Provisioning.* libraries when upstream Azure.ResourceManager.* dependencies change.

Changes:

• Introduces a new skill guide under .github/skills/ describing provisioning regeneration steps.
• Documents generator invocation, common breaking-change patterns, and follow-up validation steps.