rpc: implement DecodeAssetInvoice #3591

Job	Run time
test vector check	44s
Docker build check	3m 34s
Compilation check	41s
migration version check	11s
cross compilation	4m 50s
go mod check	23s
RPC check	1m 15s
sample configuration check	40s
Sqlc check	2m 42s
Format check	19s
run itests	9m 2s
run itests postgres	16m 39s
Lint check	2m 35s
run LiT tests	3m 51s
run unit tests (unit-race)	11m 23s
run unit tests (unit-cover)	2m 42s
run unit tests (unit dbbackend=postgres)	6m 8s
finish	2s
	1h 7m 41s

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