ci: Refactor Dockerfile & entrypoint #2441

Job	Run time
Generate crates matrix	25s
Check crates matrix	4s
Build zebrad crate	33m 36s
Build zebra-utils crate	15m 23s
Build zebra-test crate	1m 26s
Build zebra-state crate	30m 7s
Build zebra-script crate	2m 57s
Build zebra-scan crate	22m 55s
Build zebra-rpc crate	31m 49s
Build zebra-node-services crate	4m 10s
Build zebra-network crate	6m 32s
Build zebra-grpc crate	13m 17s
Build zebra-consensus crate	16m 10s
Build zebra-chain crate	5m 16s
Build tower-fallback crate	1m 45s
Build tower-batch-control crate	1m 20s
Open or update issues for building crates individually failures	0s
	3h 7m 12s

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