ci: Refactor Dockerfile & entrypoint #2561

Job	Run time
Check deny.toml bans	46s
Check deny.toml bans --features default-release-binaries	1m 9s
Check deny.toml bans --all-features	43s
Check deny.toml sources	1m 13s
Check Cargo.lock is up to date	1m 7s
Install zebrad from lockfile without cache on ubuntu-latest	9m 2s
Check deny.toml sources --features default-release-binaries	44s
Check deny.toml sources --all-features	1m 0s
Test stable on ubuntu-latest	33m 17s
Check for unused dependencies	16s
Test beta on ubuntu-latest	34m 18s
Test stable on macos-latest	36m 39s
Test stable on windows-latest	36m 30s
Test beta on windows-latest	36m 30s
Open or update issues for OS integration failures	1s
	3h 13m 15s

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