Start versioning schema files

**Is your feature request related to a problem? Please describe.**
We are deploying MAS as part of our Helm chart and want to validate user-provided configurations via the upstream MAS config schema.

Shipping a specific version of MAS requires a matching, versioned configuration schema, but currently only an unversioned schema is provided under https://element-hq.github.io/matrix-authentication-service/config.schema.json.

**Describe the solution you'd like**
Please host configuration schemas for each version of MAS, e.g., `config-v0.13.0.schema.json`, `config-v0.14.0.schema.json`, `config-v0.14.1.schema.json`, so they can be referenced by their URL and don’t change over time. Bonus points:
- Give each schema an $id that is equal to the URL where it can be retrieved.
- Make uploading new schemas part of the release automation.

**Describe alternatives you've considered**
Self-hosting adapted versions of the MAS config schema with custom $ids.