chore(cmd): clean up commands (#9705)

Move infrastructure related commands to under `cmd/infra` and
development stuff to `cmd/dev`. The default build command builds the
regular user facing binaries: syncthing, stdiscosrv, and strelaysrv.

.github/workflows/build-syncthing.yaml

@@ -516,7 +516,7 @@ jobs:
 
       - name: Install signing tool
         run: |
-          go install ./cmd/stsigtool
+          go install ./cmd/dev/stsigtool
 
       - name: Sign archives
         run: |