Add dashboard tag for charm name if it is missing

[sed-i]

Enhancement Proposal

Per ADR, it would be handy if dashboards had a tag indicating the name of the charm it came from (not the app name!).

An easy way to accomplish this with zero changes elsewhere is by adding the tag ourselves, if it is missing. We would need to do it in two places:

GrafanaDashboardProvider

grafana-k8s-operator/lib/charms/grafana_k8s/v0/grafana_dashboard.py

Lines 1135 to 1141 in 95adce2

	for path in filter(_is_dashboard, Path(self._dashboards_path).glob("*")):
	# path = Path(path)
	id = "file:{}".format(path.stem)
	stored_dashboard_templates[id] = self._content_to_dashboard_object(
	_encode_dashboard_content(path.read_bytes()), inject_dropdowns
	)
	stored_dashboard_templates[id]["dashboard_alt_uid"] = self._generate_alt_uid(id)

grafana-agent-operator

https://github.com/canonical/grafana-agent-operator/blob/efff57b4d1f3eb8bb397b58d4d2f4373bc88e474/src/grafana_agent.py#L467-L476