Add callback migrating database #58

Job	Run time
versions	1s
versions	1s
general / conventional_commits	3s
general / conventional_commits	3s
dart / dart_analyzer	51s
dart / dart_analyzer	59s
app_jobs / coverage	9m 15s
app_jobs / coverage	8m 59s
app_jobs / e2ee_test (synapse)	3m 41s
app_jobs / e2ee_test (synapse)	3m 41s
app_jobs / coverage_without_olm	12m 10s
app_jobs / coverage_without_olm	12m 11s
app_jobs / e2ee_test (dendrite)	3m 37s
app_jobs / e2ee_test (dendrite)	3m 37s
app_jobs / e2ee_test (conduit)	3m 35s
app_jobs / e2ee_test (conduit)	3m 35s
app_jobs / pub-dev-dry-run	34s
app_jobs / pub-dev-dry-run	30s
	1h 7m 23s

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