Refactor JSON responses with a reusable component

[csc-felipe]

Proposed solution

In #578, some of the JSON responses were refactored, and work could continue from there to have a reusable JSON response component.

As seen in

metadata-submitter/metadata_backend/api/handlers/restapi.py

Lines 132 to 139 in 1d3979f

	async def _json_response(data: Union[Dict, List[Dict]]) -> Response:
	"""Reusable json response, serializing data with ujson.
	:param data: Data to be serialized and made into HTTP 200 response
	"""
	return web.Response(
	body=ujson.dumps(data, escape_forward_slashes=False), status=200, content_type="application/json"
	)

DoD (Definition of Done)

Refactor endpoints returning JSON response to use a new reusable JSON response component, improving it as necessary.

Testing