Changes to Send a user message and start a run

the request's body type changed from object to no type

removed the request property text

added subschema #1 subschema #2 subschema #3 subschema #4 subschema #5 to the request body oneOf list

added the optional property message/parts/items/contentType to the response with the 201 status

added the optional property message/parts/items/fileName to the response with the 201 status

added the optional property message/parts/items/pendingAttachmentId to the response with the 201 status

added the optional property message/parts/items/sizeBytes to the response with the 201 status

endpoint added