revert(schemas): use local schema validation for rules API

[hayk96]

1. What this PR does / why we need it:

• This PR reverts the schema validation mechanism of the rules API, introduced in v0.1.2, to use a locally defined schema instead of a remote schema. Some users have reported difficulties when running the prometheus-api in an intranet environment. Therefore, this approach is prioritized over using a remotely updated schema, although the schema is not updated often.

2. Make sure that you've checked the boxes below before you submit PR:

• DCO signed
• No conflict with the main branch.