syntax errors in yml files

[jfaurskov]

Overview/Summary

Updates relevant yml files to remove syntax check errors. Described in https://dev.azure.com/CSUSolEng/Guidance%20-%20Observability/_workitems/edit/38484/

This PR fixes/adds/changes/removes

1. .github/yml-schemas/validate_yml.py is updated to handle situations where alerts.yaml is empty.
2. services/Batch/batchAccounts/alerts.yaml is updated with correct format tags
3. services/Compute/virtualMachines/alerts.yaml tags are removed since they are empty
4. services/Network/expressRouteCircuits/alerts.yaml is updated with relevant values where null as well as corrected indentation.
5. services/Network/vpnGateways/alerts.yaml is updated with references
6. Add services/Search/searchServices/Deploy-ActivityLog-SearchService-Del.json as it is missing
7. Add missing properties to services/Search/searchServices/alerts.yaml

Breaking Changes

N/A

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.)

[judyer28]

LGTM

[judyer28]

LGTM