Handling domains created as custom types or other domains

[laurenceisla]

Right now, a domain created as a data type defined in pg_catalog returns the name of the base type. No problem there, since:

create domain mydomain as int;

will be shown in OpenAPI as an integer. The problem starts when the domain is created as a custom type or as another domain. Then, postgrest-openapi treats it as a string instead of the schema defined by the base type.