Streamline and harmonize simple responses across API routes

[aleene]

What

The simple responses of various api's use different formats: "string", "message=text", "detail=text". Some are undocumented. This requires implementors to cater for all these variants.

Steps to reproduce the behavior:

Check the swagger doc.

Expected behavior

Have the same json format (like detail=text) for all simple responses.

[kirtanchandak]

working on this

[kirtanchandak]

Here we can have two options -

1. Either we can have - {"message": "No product found matching the given tags."}
2. Or - {"detail": {"msg": "missing value for k"}} this is present currently is some part of the codebase where for eg. k is not entered

related issue - #107

related PR - #234

[kirtanchandak]

@CharlesNepote @teleboas

[CharlesNepote]

IMHO, when a list is waited, and the list is empty, we should only return a JSON empty list ([]) and not a message. See my comments in #234.

@aleene?