Add CI action to publish custom-branch hydra-node docker images #6405

Job	Run time
Build & test (hydra-plutus)	1m 28s
Build & test (hydra-tui)	3m 23s
Build specification using nix	1m 25s
Benchmarks (hydra-node, tx-cost, --output-directory $(pwd)/../benchmarks)	2m 31s
Build & test (hydra-node)	9m 9s
Benchmarks (hydra-node, micro, -o $(pwd)/../benchmarks/ledger-bench.html)	1m 33s
Build & test (hydra-tx)	1m 46s
Benchmarks (hydra-cluster, bench-e2e, datasets datasets/1-node.json datasets/3-nodes.json --outpu...	4m 4s
Build & test (hydra-cluster)	10m 9s
Build haddock using nix	1m 3s
nix flake check	4m 34s
Compute cost differences	3m 49s
Publish benchmark results	6s
Publish test results	14s
Documentation	2m 39s
	47m 53s

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