feat: add _on_upgrade #859

Job	Run time
PR Region / Check against ignorelist	6s
PR Agent / Check against ignorelist	6s
PR Region / Quality Checks / Check the CHARMHUB_TOKEN secret	1s
PR Agent / Quality Checks / Check the CHARMHUB_TOKEN secret	1s
PR Region / Quality Checks / Inclusive naming / check	7s
PR Region / Quality Checks / Linting / Lint	17s
PR Region / Quality Checks / Scenario Tests / Scenario tests	19s
PR Region / Quality Checks / Static Analysis / Static Analysis of Charm	26s
PR Region / Quality Checks / Static Analysis / Static Analysis of Libs	22s
PR Region / Quality Checks / Unit Tests / Unit tests	21s
PR Agent / Quality Checks / Inclusive naming / check	5s
PR Agent / Quality Checks / Linting / Lint	24s
PR Agent / Quality Checks / Scenario Tests / Scenario tests	26s
PR Agent / Quality Checks / Static Analysis / Static Analysis of Charm	21s
PR Agent / Quality Checks / Static Analysis / Static Analysis of Libs	18s
PR Agent / Quality Checks / Unit Tests / Unit tests	22s
PR Agent / Quality Checks / Check libraries	0s
PR Region / Quality Checks / Check libraries	0s
PR Agent / Quality Checks / CodeQL analysis / Analyze (python)	1m 20s
PR Region / Quality Checks / CodeQL analysis / Analyze (python)	1m 18s
PR Region / Quality Checks / Integration Tests / Integration Tests	4m 53s
PR Agent / Quality Checks / Integration Tests / Integration Tests	13m 34s
	25m 7s

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