Document monitoring for single-region and multi-region Azure Functions

[Hou (SciencePotato)]

Summary

• Add monitoring guidance for both single-region and multi-region Azure Functions.
• Provide user KQL examples, action groups, Workbooks, alert starting points, availability guidance, and missing-telemetry detection.
• Treat Front Door as an optional routing/monitoring layer and document sampling, privacy, evaluation-mode, and ingestion limitations.
• Add a README link for discoverability.

This documentation-only PR targets main independently of the Front Door infrastructure PR #34 and the separate Application Insights explanation PR. It does not change Azure resources, monitoring configuration, or runtime code.

Validation

• Reviewed against current repository logging/setup configuration and Microsoft telemetry schemas.
• Git diff whitespace check passed.
• This newly authored guide's KQL was schema-reviewed, not live-executed.