Added alert for AI search service

[didayal-msft]

Overview/Summary

Replace this with a brief description of what this Pull Request fixes, changes, etc.

This PR fixes/adds/changes/removes

1. Add a delete activity alert rule for Microsoft.Search/searchServices as per the guidance in the article below.
   https://learn.microsoft.com/en-us/azure/search/monitor-azure-cognitive-search#azure-ai-search-alert-rules

As part of this Pull Request I have

• Read the Contribution Guide and ensured this PR is compliant with the guide
• Checked for duplicate Pull Requests
• Associated it with relevant GitHub Issues or ADO Work Items (Internal Only)
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Ensured PR tests are passing
• Updated relevant and associated documentation (e.g. Contribution Guide, Docs etc.)