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>

sources/src/configuration.ts

@@ -171,6 +171,23 @@ export class CacheConfig {
         const dvConfig = new DevelocityConfig()
         return dvConfig.getDevelocityAccessKey() !== '' || dvConfig.hasTermsOfUseAgreement()
     }
+
+    getCacheProvider(): CacheProvider {
+        const val = core.getInput('cache-provider')
+        switch (val.toLowerCase().trim()) {
+            case 'basic':
+                return CacheProvider.Basic
+            case 'enhanced':
+            case '':
+                return CacheProvider.Enhanced
+        }
+        throw TypeError(`The value '${val}' is not valid for 'cache-provider'. Valid values are: [basic, enhanced].`)
+    }
+}
+
+export enum CacheProvider {
+    Basic = 'basic',
+    Enhanced = 'enhanced'
 }
 
 export enum CacheCleanupOption {