Show milliseconds in ulog_messages timestamps

[digitalw0lf]

This PR adds milliseconds to the output of ulog_messages, since it's often useful to know precise time of events. Now it looks like this:

0:06:14.571 INFO: [dragonbee] Starting salto maneuver
0:06:14.827 INFO: [dragonbee] Salto phase: ROTATE_DOWN (z -0.207519 vz -2.052845)
0:06:15.001 INFO: [dragonbee] Salto phase: ROTATE UP

[bkueng]

Looks good. CI failure is unrelated.