Collect list of skill files

While collecting the count of files for the dashboard we should also collect the file list. We can then compare this to telemetry to see which files are actually being used.

Reference: https://github.com/microsoft/GitHub-Copilot-for-Azure/pull/2876#discussion_r3615744593

Start by finding the code that currently counts skill files for the dashboard, then review the discussion in pull request 2876. Extend the collected data to include the file list, and verify that it is available for comparison with telemetry.

Written by the indexing model from the issue text.