Support non-default parameter style and explode values

[czechboy0]

OpenAPI supports expressing quite a few different ways of encoding parameters, especially query items.

The generator currently only supports the defaults, but not the other ones.

Is needed to support e.g. foo=A,B,C in addition to the default foo=A&foo=B&foo=C.

For details, see style and explode in https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#fixed-fields-10