"Flat" mode for IG Repository

[JPercival]

• Support for IGs without type or category hierarchies (sushi style)
• Auto-detection of repository layout configuration (whether to use category directories, prefix filenames, etc.)
• Test for the above
• Moving all the IG-repo related functionality to single package and make everything possible package-private to reduce public API.

[github-actions[bot]]

Formatting check succeeded!

[codecov[bot]]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (b52ef04) 52.61% compared to head (a9aba1a) 52.86%.

Files	Patch %	Lines
...fhir/utility/repository/ig/IGRepositoryConfig.java	83.07%	4 Missing and 7 partials :warning:
...s/cqf/fhir/utility/repository/ig/IGRepository.java	88.23%	1 Missing and 3 partials :warning:
...rg/opencds/cqf/fhir/cr/cli/command/CqlCommand.java	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #422 +/- ## ============================================ + Coverage 52.61% 52.86% +0.25% - Complexity 2063 2092 +29 ============================================ Files 275 278 +3 Lines 11627 11702 +75 Branches 1584 1592 +8 ============================================ + Hits 6117 6186 +69 Misses 4907 4907 - Partials 603 609 +6 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.