Refactor/dynamite/prepare_httpclient_request_flow

[Leptopoda]

refactors extracted from: #1580
Motivation:
This decouples the resolving and generation of our parameter code.
The new code first resolves everything into a collections that can later be used to generate code.

      final operationParameters = <Parameter>[];
      final pathParameters = <openapi.Parameter, TypeResult>{};
      final headerParameters = <openapi.Parameter, TypeResult>{};

This is needed to keep further behavior changing changes easy to review.

[provokateurin]

LGTM overall

Typo in the commit message: refactor(dynamite): split mimetiype resolving and parameter generation should be refactor(dynamite): split mimetype resolving and parameter generation

Thanks for splitting this up very nicely.