`Create_Release_Git_Tag`: CI-aware, idempotent tagging, and dry-run support

[Copilot]

This PR enhances the Create_Release_Git_Tag build task with three key improvements:

1. CI-aware commit resolution

• Adds a new BuildCommit parameter that automatically resolves the commit SHA from CI environment variables
• Supports GitHub Actions (GITHUB_SHA) and Azure Pipelines (BUILD_SOURCEVERSION)
• Falls back to git rev-parse HEAD if no CI variables are available
• Ensures release tags point to the exact commit that was built/tested, avoiding issues where the tag points to a different commit than what was actually deployed

2. Idempotent tagging behavior

• Checks for existing remote tags before attempting to create new ones
• Skips tag creation if the tag already exists remotely, preventing conflicts in overlapping CI runs
• Validates that target commits exist locally and fetches them if necessary

3. Dry-run support

• Adds a new DryRun parameter (defaults to false) for testing tag operations without making changes
• When enabled, skips the actual push and verification commands
• Outputs clear messages showing what would have been done
• Returns the commit SHA that would have been tagged

Enhanced logging

• Provides detailed debug output showing the resolved commit SHA and its source
• Logs all key operations including fetching, tag creation, and verification
• Makes troubleshooting easier in CI environments

These changes maintain backward compatibility while providing more reliable and observable tag creation in CI/CD pipelines.

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