Avoid redundant DiagnosticEvents error message

[RohitRanjanMS]

Adding a validation check for the storage connection string. If the connection string is null, empty, or invalid, diagnostic events will not be written to table storage, and the service will be disabled. This will help reduce noise in the FunctionsLogs table caused by exceptions thrown due to an invalid or empty connection string.

resolves #10163

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR [in-proc] Avoid redundant DiagnosticEvents error message #10396
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)