Standardize request handlers, esp exception handling

[dennyabrain]

Which feature or component needs enhancement?
All request handlers associated with routes.

Describe the current behavior
There are route handlers that only have the happy path of a request handling flow.
For instance

kaapi-guardrails/backend/app/api/routes/ban_lists.py

Lines 14 to 27 in 1d62fc2

	@router.post(
	"/",
	description=load_description("ban_lists/create_ban_list.md"),
	response_model=APIResponse[BanListResponse],
	)
	def create_ban_list(
	payload: BanListCreate,
	session: SessionDep,
	auth: MultitenantAuthDep,
	):
	ban_list = ban_list_crud.create(
	session, payload, auth.organization_id, auth.project_id
	)
	return APIResponse.success_response(data=ban_list)

Describe the enhancement you'd like
Finalize a syntax for status response messages and the amount of information to include in them and start adding some exception handlers to the request handler functions.

Why is this enhancement needed?
The kaapi team and any downstream API users of kaapi API will get meaningful error messages.