replace go mod statements for api and sdk (#1146)

go.mod

@@ -2,6 +2,10 @@ module github.com/hashicorp/boundary
 
 go 1.16
 
+replace github.com/hashicorp/boundary/api => ./api
+
+replace github.com/hashicorp/boundary/sdk => ./sdk
+
 require (
 	github.com/armon/go-metrics v0.3.6
 	github.com/bufbuild/buf v0.37.0