feat(cmd-api-server): swagger.json endpoints

[petermetz]

Is your feature request related to a problem? Please describe.

The API server currently does not have the ability to serve up the swagger.json (openapi.json) files via HTTP

Describe the solution you'd like

• Each plugin should have a dedicated endpoint that returns the OpenAPI spec json file.
• The API server itself should also do the same for it's own services
• The web service plugins all need to be updated to contain an endpoint that does the serving of the file
• The code for this web service should be somehow reused across plugins instead of being copy pasted over to each and every one of them. Probably the cactus-core package is a good place to start, but this might not be the best solution, make sure to check.

Describe alternatives you've considered

This https://github.com/hyperledger/cactus/issues/431 They are not mutually exclusive, but wanted to reference the other task here just for providing more complete information to the reader.

Additional context

We need the serving of the OpenAPI spec files for various reasons, one of them is that our fuzzer could leverage that for targeted scanning in a completely automated way which would be really great for us.

[charellesandig]

Hi @petermetz I'll be working on this one, thank you!