feat(build): use -facade-group=client in rebuild-schema makefile target

The schemas output for python-libjuju should not have contained any
non-client schemas (see this python-libjuju issue
juju/python-libjuju#1099). Switching to only
the client schemas reduces the amount of generated code in
python-libjuju substantially.

Makefile

@@ -497,9 +497,9 @@ rebuild-schema:
 	@echo "Generating facade schema..."
 # GOOS and GOARCH environment variables are cleared in case the user is trying to cross architecture compilation.
 ifdef SCHEMA_PATH
-	@env GOOS= GOARCH= go run $(COMPILE_FLAGS) $(PROJECT)/generate/schemagen -admin-facades "$(SCHEMA_PATH)"
+	@env GOOS= GOARCH= go run $(COMPILE_FLAGS) $(PROJECT)/generate/schemagen -admin-facades -facade-group=client "$(SCHEMA_PATH)"
 else
-	@env GOOS= GOARCH= go run $(COMPILE_FLAGS) $(PROJECT)/generate/schemagen -admin-facades \
+	@env GOOS= GOARCH= go run $(COMPILE_FLAGS) $(PROJECT)/generate/schemagen -admin-facades -facade-group=client \
 		./apiserver/facades/schema.json
 endif