Add `vip app deploy validate` command for Custom Deployments (#1886) #3209

Job	Run time
Verify signatures and provenance statements	34s
Lint	40s
Type Checker	45s
Dependaban	10s
Check formatting	36s
Run tests (lts/*)	31s
Run tests (lts/-1)	29s
Run tests (current)	38s
	4m 23s

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