feat: As a user, I want to include the request body in the opa-input, so that I can reason about its contents

### Description

The opa-plugin already includes various information about the http-request(path, query, headers etc.) in the opa-input. However, its not possible to also include the request body as part of the input. This would extend OPAs capabilities in terms of decision making, f.e. to check if only allowed fields of a certain entity are manipulated within a PUT request.