Add body_suffix parameter to include VS Code header in coding agent PRs

[Copilot]

This PR implements the body_suffix parameter when creating coding agent sessions to add a VS Code header to PRs created by the GitHub Copilot coding agent.

Changes Made

Modified src/github/copilotRemoteAgent.ts:

• Added body_suffix parameter to the RemoteAgentJobPayload in the invokeRemoteAgent method
• The header provides professional attribution with links to official documentation

Expected Behavior

When users create pull requests via the copilot coding agent, the PR description will now include a professional footer:

---

*This pull request was created by the [GitHub Copilot coding agent](https://docs.github.com/en/copilot/using-github-copilot/coding-agent) via [GitHub Pull Requests](https://marketplace.visualstudio.com/items?itemName=GitHub.vscode-pull-request-github) for VS Code.*

This provides clear attribution and helps users understand the source of automatically generated PRs while maintaining professional presentation with clickable links to relevant documentation and the VS Code extension marketplace.

Technical Details

The body_suffix parameter was already defined in the RemoteAgentJobPayload interface but was not being utilized. This change adds the parameter to the payload construction, ensuring that all PRs created through the coding agent will include the VS Code attribution footer.

The implementation preserves all existing functionality and conditional logic (such as the head_ref parameter for cases with pending changes).

Fixes #7225.

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[joshspicer]

@copilot you don't need this part

This pull request was created by the GitHub Copilot coding agent

[Copilot]

@copilot you don't need this part

This pull request was created by the GitHub Copilot coding agent

Removed the GitHub Copilot coding agent reference from the body_suffix. The PR footer now includes only the VS Code attribution. (87b1afb)