Changes to Create session-student relationship

added the optional property items/id to the response with the 201 status

added the new required request property session_ids

added the new required request property student_ids

the response's body type changed from object to array for status 201

removed the required property created_at from the response with the 201 status

removed the required property present from the response with the 201 status

removed the required property session_id from the response with the 201 status

removed the required property student_id from the response with the 201 status

removed the required property updated_at from the response with the 201 status

removed the request property session_id

removed the request property student_id

removed the optional property notes from the response with the 201 status

endpoint added