build: add release-install goal, hash individual binaries

We add a new make goal called release-install that creates the same
reproducible binaries as the release script would create, but only for
the current OS/architecture. It then installs those binaries to the
system's GOBIN directory.
To allow easy verification of individual binaries (instead of just the
packag tarballs/zips), we also add the hashes of lnd and lncli binaries
to the manifest. We do the same in the docker build.

Makefile

@@ -151,6 +151,11 @@ install:
 	$(GOINSTALL) -tags="${tags}" $(LDFLAGS) $(PKG)/cmd/lnd
 	$(GOINSTALL) -tags="${tags}" $(LDFLAGS) $(PKG)/cmd/lncli
 
+release-install:
+	@$(call print, "Installing release lnd and lncli.")
+	env CGO_ENABLED=0 $(GOINSTALL) -v -trimpath -ldflags="$(RELEASE_LDFLAGS)" -tags="$(RELEASE_TAGS)" $(PKG)/cmd/lnd
+	env CGO_ENABLED=0 $(GOINSTALL) -v -trimpath -ldflags="$(RELEASE_LDFLAGS)" -tags="$(RELEASE_TAGS)" $(PKG)/cmd/lncli
+
 release:
 	@$(call print, "Releasing lnd and lncli binaries.")
 	$(VERSION_CHECK)