feat: use external_url in grafana source (#632) #64

Job	Run time
release / Quality Checks / Check the CHARMHUB_TOKEN secret	1s
release / Quality Checks / Linting / Lint	10s
release / Quality Checks / Inclusive naming / check	5s
release / Quality Checks / Scenario Tests / Scenario tests	27s
release / Quality Checks / Static Analysis / Static Analysis of Charm	27s
release / Quality Checks / Static Analysis / Static Analysis of Libs	22s
release / Quality Checks / Unit Tests / Unit tests	31s
release / Quality Checks / Check libraries	26s
release / Quality Checks / CodeQL analysis / Analyze (python)	2m 13s
release / Quality Checks / Integration Tests / Integration Tests	51m 59s
release / Release any bumped charm library	27s
release / Release Charm and Libraries / Build the charms	9m 27s
release / Release Charm and Libraries / Build the charms for ARM	0s
release / Release Charm and Libraries / Release arm64 to CharmHub	0s
release / Release Charm and Libraries / Release to CharmHub (prometheus-k8s_ubuntu-20.04-amd64.charm)	7m 14s
release / Release Charm and Libraries / Charm List	0s
	1h 13m 49s

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