[Documentation] Things To Add

This issue will remain locked and serves only as a reminded to myself of what I still need to add to the documentation.
- [x] Console commands, `api:cache`, `api:routes`, and `api:docs`.
- [x] API Blueprint Documentation
- [x] Controller helper trait needs a good overview, currently it's mentioned in various sections.
- [ ] More details on custom extenders, e.g., transformer adapters, rate limit throttles, authentication providers, etc.
- [x] More details on how exceptions are handled and the best way to report errors.
- [x] Dealing with exceptions and error responses in internal requests.
- [x] Generating URLs
- [x] A page on more complex configuration, e.g., custom validators, etc.
- [ ] FormRequest
- [ ] Using throttles on routes/controllers/groups.

If you find any issues with the documentation please open an issue on the [dingo/api-docs](https://github.com/dingo/api-docs) repository instead of here. Much appreciated!