Add JSON Schemas for features

[ppkarwasz]

This change documents the available .asf.yaml options as composable draft-07 JSON Schemas.

Since features live in separate Python modules, the schemas are composable too: each feature's schema sits next to the module that validates it (e.g. asfyaml/feature/notifications.schema.json, asfyaml/feature/github/rulesets.schema.json), and the root asfyaml/asfyaml.schema.json wires them together through relative $refs. The $id of every file is its raw.githubusercontent.com URL and mirrors its path in the repository, so refs resolve both on disk and over HTTP. Editors can therefore validate a repository's .asf.yaml with a single comment:

# yaml-language-server: $schema=https://raw.githubusercontent.com/apache/infrastructure-asfyaml/refs/heads/main/asfyaml/asfyaml.schema.json

Coverage matches the current validators on main: all root keys (meta, notifications, project, github, pelican, jekyll, publish, staging), the full github feature set (branch protection, rulesets in both raw and convenience styles, deployment environments, merge buttons, custom subjects, pull requests, Copilot code review, etc.), and constraints that are only enforced at runtime today (enums, label limits, wait_timer range, ASF mailing list pattern).

A new test module (tests/json_schema.py) checks every schema against the draft-07 metaschema, enforces the $id/path mirroring, and validates known-good and known-bad .asf.yaml samples with all refs resolved offline. jsonschema is added as a test-only dependency.

[ppkarwasz]

@netomi,

Personally I would like to validate the .asf.yaml schemas against JSON schemas published to infra.apache.org, but I would settle on apache.github.io. Where should I put the schema files in this repo's folder hierarchy?

[potiuk]

Nice. I think this schema could also be used to validate asf.yaml when it is parsed. And I think - keeping the schema in here in github with "raw" URL is probably not a bad idea?