rpc: implement DecodeAssetInvoice #3622

Job	Run time
Docker build check	3m 34s
cross compilation	3m 42s
Compilation check	41s
Format check	22s
run itests	9m 32s
run itests postgres	17m 29s
Lint check	6m 44s
go mod check	24s
migration version check	10s
RPC check	1m 20s
run LiT tests	9m 41s
sample configuration check	30s
Sqlc check	35s
test vector check	41s
run unit tests (unit-race)	11m 27s
run unit tests (unit-cover)	2m 25s
run unit tests (unit dbbackend=postgres)	6m 9s
finish	4s
	1h 15m 30s

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