Add versioned schemas and PR validation for index.json files

[jormundur00]

What does this PR do?

This PR introduces versioned schemas for all existing index.json files in the repository and adds a workflow to validate any changed index.json files in a pull request against their respective schemas.

Currently, there are four types of index.json files:

1. Global metadata index.json

   • Located at metadata/index.json

2. Library metadata index.json

   • Located at metadata/<groupId>/<artifactId>/index.json for each library in the repository

3. Global tests index.json

   • Located at tests/src/index.json

4. Optional test sub-project index.json

   • Located at tests/src/<groupId>/<artifactId>/<version>/index.json
   • Currently, only the example library uses this structure

---

Additional Changes

• The following schemas are now packaged with all future releases of GraalVM Reachability Metadata:

  • schemas/metadata-root-index-schema-v1.0.0.json
  • schemas/metadata-library-index-schema-v1.0.0.json
  • schemas/library-and-framework-list-schema-v1.0.0.json

  These are used in Native Build Tools to detect potential mismatches between metadata and build tools versions.

---

Fixes: #813

[vjovanov]

We should always strive to do this in gradle. That way I can also do it locally to verify everything is OK.

[jormundur00]

Makes sense. I've removed this file-producing part of the GitHub action and created a generateChangedIndexFileMatrix gradle task that will do this in gradle (and is locally test-able). As these tasks require a ci.json entry, I've added it as only tested on java: latest-ea and os: ubuntu-latest as not to produce multiple jobs (because there shouldn't be any change with different jdks for this functionality as we don't run native-image).