Rework `SUPERVISOR_COMMS.send_request` class/method to have `log` stored as a attribute

[kaxil]

          This reminds me: we should rework this class/method to have `log` stored as a attribute so we don't need to pass log in to this class.

(Future work; doing this will make it easier to use this from within XCom or Variable class.)

Originally posted by @ashb in #44590 (comment)