docker-compose: move signdald to different docker-compose

when developing metamigo you want to run the api, frontend, and worker
locally but want postgres and signald in containers.

this commit moves signald into the postgresql compose (which could be
renamed now i suppose) so you can run just that compose (npm run
docker:metamigo:dev:up) to do local dev on metamigo.

docker-compose.metamigo-postgresql.yml

@@ -1,7 +1,12 @@
 version: "3.4"
 
+x-global-vars:
+  &common-global-variables
+  TZ: Etc/UTC
+
 x-metamigo-vars:
   &common-metamigo-variables
+  <<: *common-global-variables
   DATABASE_HOST: "metamigo-postgresql"
   DATABASE_NAME: "metamigo"
   DATABASE_ROOT_OWNER: "root"
@@ -48,6 +53,17 @@ services:
     ports:
       - 127.0.0.1:5433:5432
 
+  signald:
+    container_name: signald
+    build: ./docker/signald
+    image: registry.gitlab.com/digiresilience/link/link-stack/signald:${LINK_STACK_VERSION}
+    restart: ${RESTART}
+    user: ${CURRENT_UID}
+    volumes:
+      - ./signald-state:/signald
+    environment:
+      <<: *common-global-variables
+
 volumes:
   metamigo-data:
     driver: local