update cert_handler charm lib to version that has stable hashes

[ca-scribner]

Enhancement Proposal

#15 includes a local fix to the cert_handler library to fix an issue with the hashing of cert input config

istio-ingress-k8s-operator/lib/charms/observability_libs/v1/cert_handler.py

Lines 446 to 456 in ab1fda9

	def _csr_hash(self) -> str:
	"""A hash of the config that constructs the CSR.
	Only include here the config options that, should they change, should trigger a renewal of
	the CSR.
	TODO: This is a custom _csr_hash implementation that fixes a bug where the old hash was session dependent.
	It should be pushed to the library and then we should import the new version.
	"""
	immutable_config = (str(self.sans_dns) + str(self.sans_ip)).encode("utf-8")
	return hashlib.sha256(immutable_config).hexdigest()

This was required because previously the hashing was python session dependent, meaning sequential charm calls generated different hash values for the same inputs. The cert_handler recently received a similar fix, but it removed the refresh_events feature which we rely on here so we cannot immediately update to the new library. To fix this, we need to restore the refresh_events feature in cert_handler or find a new pattern to use here.