Add a Nix flake #2099

Job	Run time
Generate crates matrix	8s
Check crates matrix	6s
Build zebrad crate	39m 14s
Build zebra-utils crate	17m 24s
Build zebra-test crate	1m 33s
Build zebra-state crate	23m 35s
Build zebra-script crate	3m 46s
Build zebra-scan crate	26m 40s
Build zebra-rpc crate	34m 34s
Build zebra-node-services crate	3m 8s
Build zebra-network crate	6m 46s
Build zebra-grpc crate	14m 48s
Build zebra-consensus crate	16m 54s
Build zebra-chain crate	4m 56s
Build tower-fallback crate	1m 4s
Build tower-batch-control crate	1m 29s
Open or update issues for building crates individually failures	0s
	3h 16m 5s

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