Implement `grafana_datasource_exchange` #976

Job	Run time
PR / Check against ignorelist	7s
PR / Quality Checks / Check the CHARMHUB_TOKEN secret	1s
PR / Quality Checks / Linting / Lint	22s
PR / Quality Checks / Static Analysis / Static Analysis of Charm	35s
PR / Quality Checks / Scenario Tests / Scenario tests	32s
PR / Quality Checks / Inclusive naming / check	5s
PR / Quality Checks / Static Analysis / Static Analysis of Libs	38s
PR / Quality Checks / Unit Tests / Unit tests	1m 2s
PR / Quality Checks / Check libraries	28s
PR / Quality Checks / CodeQL analysis / Analyze (python)	1m 21s
PR / Quality Checks / Integration Tests / Integration Tests	1h 23m 6s
	1h 28m 17s

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