[custom channels]: generate unique script keys for HTLCs #3501

Job	Run time
Docker build check	3m 37s
Format check	45s
cross compilation	3m 31s
Compilation check	50s
run itests	9m 30s
run itests postgres	19m 9s
Lint check	2m 16s
go mod check	43s
RPC check	1m 36s
migration version check	14s
run LiT tests	11m 48s
sample configuration check	39s
Sqlc check	41s
test vector check	53s
run unit tests (unit-race)	11m 58s
run unit tests (unit-cover)	2m 10s
run unit tests (unit dbbackend=postgres)	5m 10s
finish	3s
	1h 15m 33s

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