bug(experimenter): make glean writes to stdout more atomic

[relud]

Because

• In prod glean pings are coming out as {ping}{ping}\n\n instead of {ping}\n{ping}\n and markh suggested this might fix it

This commit

• Overrides the glean generated emit_record methods to use stdout.write(f"{ping}\n") instead of print(ping)

Fixes #13893

[relud]

if this works, we should move the change upstream to glean-parser, and revert it here when we pick up the change

[relud]

the original method is:

 def emit_record(self, now: datetime, ping:dict[str, Any]) -> None:
        """Log the ping to STDOUT.
        Applications might want to override this method to use their own logging.
        If doing so, make sure to log the ping as JSON, and to include the
        `Type: GLEAN_EVENT_MOZLOG_TYPE`."""
        ping_envelope = {
            "Timestamp": now.isoformat(),
            "Logger": "glean",
            "Type": GLEAN_EVENT_MOZLOG_TYPE,
            "Fields": ping,
        }
        ping_envelope_serialized = json.dumps(ping_envelope)

        print(ping_envelope_serialized)

[yashikakhurana]

Thanks @relud