Add instructions for Compute PR agent

[audreyttt]

Updated agent configuration for compute PowerShell pull requests, detailing objectives, rules, and required artifacts.

Description

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • General release
  • Public preview
  • Private preview
  • Engineering build
  • No need for a release

• Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd]

Thanks for your contribution! The pull request validation has started. Please revisit this comment for updated status.

[Copilot]

Pull request overview

This PR introduces a new agent configuration file that provides detailed instructions for creating PowerShell pull requests in the Azure Compute module. The agent serves as a guide for implementing new features in PowerShell cmdlets, covering everything from parameter authoring to test creation.

Key Changes:

• Adds comprehensive instructions for modifying Compute PowerShell cmdlets
• Establishes rules for parameter authoring, execution flow, and file structure
• Defines required artifacts including code changes, documentation, tests, and changelog updates

[Copilot]

[nitpick] The help regeneration command should be formatted as a code block for clarity and to prevent line wrapping issues. Consider wrapping the command in backticks or a code fence.

Suggested change

	- Regenerate using the module's help script: Update-MarkdownHelp -Path ./src/Compute/Compute/help/New-AzVM.md -AlphabeticParamsOrder -UseFullTypeName
	- Regenerate using the module's help script:
	```
	Update-MarkdownHelp -Path ./src/Compute/Compute/help/New-AzVM.md -AlphabeticParamsOrder -UseFullTypeName
	```

[isra-fel]

Ref: https://docs.github.com/en/copilot/concepts/agents/coding-agent/about-custom-agents