Changes to GET /v1/credits

added the required property usage_by_api_key/items/expires_at to the response with the 200 status

added the required property usage_by_api_key/items/period_spend to the response with the 200 status

added the required property usage_by_api_key/items/period_start to the response with the 200 status

added the required property usage_by_api_key/items/spend_limit to the response with the 200 status

added the required property usage_by_api_key/items/spend_limit_period to the response with the 200 status