Consider changing RootPathFilter to accept pattern matching

[jlperkins]

We have a request to change RootPathFilter's accepted values from a semicolon-separated list of path prefixes, to file matching patterns. This would help 1ES PT to seamlessly route through the correct files for validation for customers that download pipeline artifacts. This would be a breaking change for us if we replace RootPathFilter. We could consider adding a new option instead of replacing this one, to avoid introducing a breaking change.