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>

.github/workflows/demo-job-summary.yml

@@ -132,6 +132,23 @@ jobs:
       working-directory: .github/workflow-samples/kotlin-dsl
       run: ./gradlew assemble
 
+  basic-caching:
+    needs: build-distribution
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+    - name: Initialize integ-test
+      uses: ./.github/actions/init-integ-test
+
+    - name: Setup Gradle
+      uses: ./setup-gradle
+      with:
+        cache-provider: basic
+    - name: Build kotlin-dsl project
+      working-directory: .github/workflow-samples/kotlin-dsl
+      run: ./gradlew assemble
+
   terms-of-use-accepted:
     needs: build-distribution
     runs-on: ubuntu-latest