Implement export telemetry

[jezdez]

This PR implements telemetry for the conda export command and updates the project dependencies to rely on recent conda features.

Changes

• Export Telemetry: Added a conda_post_commands hook to capture usage data for conda export. This tracks the export format, file specification, and channel usage without capturing PII.
• Code Cleanup: Removed try-except blocks for importing CondaPostCommand and other types, as well as the NULL constant fallback, now that we can rely on the modern conda.plugins and conda.common.constants namespaces.
• Documentation: Updated faq.md and manual_testing.md to reflect the new telemetry capabilities.

Testing

• Verified conda export triggers the telemetry HEAD request locally with verbose logging.
• Existing tests updated and passed with pytest.