Changes to GET /stats/response-time

the trend/items/periodDate response's property type changed from string to string null, and format from no format to date-time for status 200

api operation id getStatsResponseTime was added

the security scope STATS_READ was added to the endpoint's security scheme ApiKeyAuth

added the non-success response with the status 400

added the non-success response with the status 401

added the non-success response with the status 403

added the non-success response with the status 405

added the non-success response with the status 429

added the non-success response with the status 500