Implemented the missing Database endpoints (#8)

This PR contains the work done to declare the missing, non-GET endpoints of the *Database* section in the [Discogs API documentation](https://www.discogs.com/developers#page:database) into the `OpenAPI` specification document.

Furthermore, documentation extensions have been defined for the `APIProtocol` and `Client` types in the `DocC` documentation catalog to match the categories of these endpoint calls to the categories in the Discogs documentation.

Reviewed-on: #8
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

docs/data/documentation/discogsservice/operations/getreleaserating/id.json

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