Remove Resource Hooks

[bart-degreed]

We've been announcing for some time that we were abandoning "Resource Hooks", an experimental feature we introduced in v4 alpha versions. In v4.2 we added alternative extensibility points, which we believe are superior in terms of clarity, simplicity, performance, and scalability.

This issue concerns deleting resource hooks from the codebase (everything in JsonApiDotNetCore.Hooks namespace, IJsonApiOptions.EnableResourceHooks/LoadDatabaseValues), along with its documentation, code examples, wiki articles, etc.