Add open-source 'basic' cache provider and revamp licensing documentation (#930)

## Summary

- **New `basic` cache provider**: Adds an open-source (MIT-licensed)
caching implementation built on `@actions/cache` as an alternative to
the proprietary Enhanced Caching. Users can opt in with `cache-provider:
basic` on both `setup-gradle` and `dependency-submission` actions.
- **Revamped licensing & distribution docs**: Replaces the verbose
licensing notice block (previously shown in README, docs, and logs) with
a friendlier callout and a new dedicated
[DISTRIBUTION.md](./DISTRIBUTION.md) covering component licensing, usage
tiers, data privacy ("Safe Harbor"), and opt-out instructions.
- **Improved messaging**: Enhanced Caching and Basic Caching each
display concise, informative log messages and job summary notes instead
of the previous wall-of-text license warning.
- **New integration tests**: Adds `integ-test-basic-cache-provider.yml`
workflow that seeds and verifies the basic cache provider across
platforms, plus unit tests for `BasicCacheService` and `getCacheService`
selection logic.
- **CI workflow reorganization**: Dependency-submission integration
tests extracted into their own reusable suite
(`suite-integ-test-dependency-submission.yml`); sample project tests
moved into the caching suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dependency-submission/action-types.yml

@@ -14,6 +14,12 @@ inputs:
     type: string
 
   # Cache configuration
+  cache-provider:
+    type: enum
+    allowed-values:
+      - basic
+      - enhanced
+
   cache-disabled:
     type: boolean
 

dependency-submission/action.yml

@@ -26,6 +26,14 @@ inputs:
     required: false
 
   # Cache configuration
+  cache-provider:
+    description: |
+      Specifies the caching implementation to use.
+      'enhanced' (default) uses the full-featured commercial caching service (gradle-actions-caching).
+      'basic' uses a simple open-source caching implementation based on GitHub Actions cache.
+    required: false
+    default: 'enhanced'
+
   cache-disabled:
     description: When 'true', all caching is disabled. No entries will be written to or read from the cache.
     required: false