add support for reading more secrets from files #1911

Job	Run time
Test and deploy (1.21, ubuntu-latest, true)	12m 38s
Test build flags	25s
Test with PgSQL/MySQL/Cockroach	18m 7s
Test and deploy (1.21, macos-latest, true)	12m 59s
Test and deploy (1.21, windows-latest, false)	18m 43s
golangci-lint	52s
Build Linux packages (amd64, ubuntu:18.04, latest, amd64)	2m 51s
Build Linux packages (aarch64, ubuntu18.04, latest, arm64)	15m 52s
Build Linux packages (ppc64le, ubuntu18.04, latest, ppc64le)	14m 59s
Build Linux packages (armv7, ubuntu18.04, latest, arm7)	17m 3s
	1h 54m 29s

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