Fix #403 : Add YAML schemas for components, tests, and metadata .

[kishansinghifs1]

Add YAML schemas for components, tests, and metadata : #403

• Added JSON schemas and component templates to define and enforce the expected YAML structure.
• Configured mappings so the Red Hat YAML extension provides autocompletion, hover docs, and inline validation when editing these files.
• The component template schema documents the expected Docker Compose service fragment structure; note that Jinja2 template syntax ({{ }}, {% %}) will still produce warnings in the editor since it's not valid YAML.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[precice-bot]

This pull request has been mentioned on preCICE Forum on Discourse. There might be relevant details there:

https://precice.discourse.group/t/gsoc-2026-kishan-singh-system-tests-improvements/2775/1