Changes to Add students to a group

added the new already_in_path enum value to the data/items/anyOf[subschema #2: BatchFailedItem]/error/code response property for the response status 200

added the new already_in_path enum value to the data/items/anyOf[subschema #2: BatchFailedItem]/error/code response property for the response status 207

added the non-success response with the status 406

added the non-success response with the status 413

added the non-success response with the status 415

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 200

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 207

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 400

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 401

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 403

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 404

media type application/json was changed to a more specific media type application/vnd.api+json for the response status 422