Alternative to SIGHUP for recurringly updating metrics for basebackups

[MPV]

Since Kubernetes doesn't support sending signals (i.e. SIGHUP) to pods/containers, it would be nice being able to trigger/schedule updates of metrics related to basebackups

Related to this in the current implementation:

wal-g-prometheus-exporter/exporter.py

Lines 296 to 300 in b5a0a46

	# Launch exporter
	exporter = Exporter()
	# listen to SIGHUP signal
	signal.signal(signal.SIGHUP, exporter.update_basebackup)

&

wal-g-prometheus-exporter/exporter.py

Lines 162 to 166 in b5a0a46

	def update_basebackup(self, *unused):
	"""
	When this script receive a SIGHUP signal, it will call backup-list
	and update metrics about basebackups
	"""

What do you think?