Basic support for overlay databases #3879

Job	Run time
Diagnostic export (windows-latest, linked)	4m 27s
Diagnostic export (ubuntu-latest, linked)	59s
Diagnostic export (macos-latest, linked)	1m 8s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 3s
Diagnostic export (macos-latest, nightly-latest)	1m 34s
Diagnostic export (windows-latest, nightly-latest)	3m 51s
	13m 2s

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