Add CrudRestApiBuilder to @loopback/rest-crud

[bajtos]

This is a follow-up for the spike #2738, see #3617.

Implement a model-api builder for CRUD REST API pattern - add CrudRestApiBuilder to @loopback/rest-crud. Modify README, rework "Basic use" to show how to use the package together with ModelApiBooter to go from a model to REST API. Move the current content of "basic use" into a new section, e.g. "Advanced use".

See the PoC implementation in the spike for inspiration.

Prerequisites:

• Implement TestSandbox.writeTextFile Implement TestSandbox.writeTextFile #3731
• Improve defineCrudRestController to create a named controller class Improve defineCrudRestController to create a named controller class #3732
• Add defineCrudRepositoryClass - a helper to create a named repository class Add defineCrudRepositoryClass - a helper to create a named repository class #3733
• Model API booter & builder Model API booter & builder #3736

Acceptance criteria

• Implementation
• API docs
• Automated tests
• Updated README