[chore][fileconsumer] Move file finding and filtering into subpackage

[djaglowski]

This PR extracts all file finding, sorting, and filtering into a dedicated matcher package.

• The matcher package is exported, as it contains several config structs. However, much of the code is further delegated to internal packages.
• Simplifies config struct unmarshaling, without any user-facing changes to config
• Deprecates corresponding config structs in fileconsumer package
• Hardens configuration validation
• Ensures that when sortation fails on some files, others can still be read
• Ensures that files that can not be sorted are not read
• Verbose error communication when files cannot be sorted
• 100% test coverage across matcher package and its internal packages