Add heartbeat for usage collection and update to Loki 3.3

[Michaelvll]

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh

[cblmemo]

Is this variable used?

[cblmemo]

a little bit curious why we need this interval seconds argument. Doesnt skylet already has a interval mechanism..?

skypilot/sky/skylet/events.py

Lines 46 to 56 in 061d4bd

	def run(self):
	self._n = (self._n + 1) % self._event_interval
	if self._n % self._event_interval == 0:
	logger.debug(f'{self.__class__.__name__} triggered')
	try:
	self._run()
	except Exception as e: # pylint: disable=broad-except
	# Keep the skylet running even if an event fails.
	logger.error(f'{self.__class__.__name__} error: {e}')
	with ux_utils.enable_traceback():
	logger.error(traceback.format_exc())