Add linter for OpenAPI spec into CI

Currently, when running the OpenAPI draft through both swagger editor and a bunch of other linters (Spectral, ibm-openapi-validator) it produces errors.

Description

Currently, when running the OpenAPI draft through both swagger editor and a bunch of other linters (Spectral, ibm-openapi-validator) it produces errors.

This causes certain issues, foremost is the fact that most OpenAPI parsing libraries will abort parsing when encountering errors. This is bad, since we want to use these libraries for both validation and later on, for code generation.

There is also currently an endpoint which breaks the HTTP standard (GET Request with request body). Such endpoints have undefined semantics according to the HTTP 1.1 standard.

To greatly reduce time spent designing the Draft according to spec and figuring out errors after the fact, we should add in depth linting support to the projects CI pipeline

Expected Behavior

OpenAPI specs that end up in master / main should be linted and produce no 'error' warnings anymore.

Actual Behavior

The OpenAPI draft that was checked in produces errors that are not trivial to fix without changing large parts of the draft.

Steps to Reproduce

Paste the current draft into the OpenAPI Editor here: https://editor.swagger.io

Context

tl;dr: This issue produces too much idle time, that could be used on new features.

This makes code generation or performing any automated operations on or by the spec REALLY hard and difficult, but I cannot change the spec, since that breaks support for the backend.