Implement code generator that takes OpenAPI and generates zio.http.api.API code

[jdegoes]

Is your feature request related to a problem? Please describe.

Some companies begin with OpenAPI, and then proceed to implement a server that satisfies the OpenAPI specification; then they will modify the OpenAPI specification when a change is necessary, and then re-implement the server.

Describe the solution you'd like

In order to support this spec-first driven approach to API development (rather than code-first, which is the paradigm already implemented within the zio.http.api package), we will need a code generator, which can read in OpenAPI specification, and generate the corresponding zio.http.API values that declaratively describe the APIs.

Then a user can implement handlers based on the code-generated API values.