Clarify POST /connection response

[sajith]

While working on #225, I came across this:

sdx-controller/sdx_controller/swagger/swagger.yaml

Lines 143 to 156 in 81df847

	requestBody:
	description: order placed for creating a connection
	content:
	application/json:
	schema:
	$ref: '#/components/schemas/connection'
	required: true
	responses:
	"200":
	description: successful operation
	content:
	application/json:
	schema:
	$ref: '#/components/schemas/connection'

It appears that both POST /connection request body and the response are supposed to follow #/components/schemas/connection schema. We have not been doing that in the responses so far anyway: we've just been returning 200 success messages without a full JSON body that follows the schema. (And even if we do it right now, we won't be really honest about things like timestamp, start_time, end_time, etc.)

This is probably worth reconsidering, and I'm creating this issue as a reminder to ourselves.

If we care about this, we probably can turn on strict validation of requests and responses (with connexion.App(strict_validation=True, validate_responses=True).