taprpc+multi: concert `taprpc` into a versioned Go module #3086

Job	Run time
Sqlc check	33s
go mod check	22s
test vector check	44s
RPC check	3m 38s
Compilation check	53s
Docker build check	3m 3s
cross compilation	4m 20s
Format check	19s
run itests	7m 45s
Lint check	3m 38s
run itests postgres	16m 28s
migration version check	15s
sample configuration check	34s
run unit tests (unit-race)	6m 44s
run unit tests (unit-cover)	2m 27s
run unit tests (unit dbbackend=postgres)	4m 42s
finish	7s
	56m 32s

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