Drop metric source gen, avoid empty tags

[jviau]

Issue describing the changes in this PR

resolves #11399

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
• 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)

Additional information

This PR's goal is to avoid emitting of metric tags when the tag value is null or empty. To accomplish this I had to drop usage of metric source gen, as it had no way to do that. Honestly, it is not a big loss -- writing these types manually is about just as much work if not less.

[Copilot]

Pull Request Overview

This PR removes the metric source generation for health check metrics and implements manual histogram classes to avoid emitting empty or null metric tags. The change transitions from auto-generated metric types to manual implementations that can conditionally exclude tags based on whether their values are null or empty.

• Replaced source-generated histogram types with manual implementations
• Added conditional tag filtering to prevent empty tags from being emitted
• Moved metric value conversion logic into the main metrics class

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
HealthCheckMetricsGeneration.cs	Removed entire file containing source-generated metric types and extension methods
HealthCheckMetrics.cs	Added manual histogram implementations with conditional tag filtering and moved helper methods
launchSettings.json	Added launch configuration for test project (unrelated to core changes)