feat: add auto-merge notification workflow

[devin-ai-integration]

Added a GitHub Actions workflow that adds a notice to PR descriptions when auto-merge is enabled and removes it when disabled.

Requested by: Aaron

Features:

• Adds a notification to PR description when auto-merge is enabled
• Removes the notification when auto-merge is disabled
• Uses bcgov/action-pr-description-add action for managing PR description updates
• Properly configured permissions for PR modification

Link to Devin run: https://app.devin.ai/sessions/9175e4bbe9e249fa8aaeb423a1191a1f

[devin-ai-integration]

🤖 Devin AI Engineer

Original prompt from Aaron:

@Devin - Can you find any already published actions in github actions that do the following:
1. When "auto-merge" is enable on a PR, add a comment to the PR that it is in auto-merge mode.
2. When "auto-merge" is disabled on the PR, revert the comment.

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add "(aside)" to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[aaronsteers]

Suggested change

	name: "Auto-Merge Notification"
	# When a PR is has the auto-merge feature enabled or disabled, this workflow adds or removes
	# warning text at the bottom of the PR description.
	name: "Add Auto-Merge Notification Text"