feat(db): use pgautoupgrade instead of custom pg_upgrade entrypoint

Replace the hand-rolled entrypoint.postgres.sh.tmpl (which apt-installed
the old PG binaries and ran initdb + pg_upgrade --link by hand) with the
pgautoupgrade/pgautoupgrade:18-alpine image, matching the other recipes.
PGDATA is pinned to the legacy /var/lib/postgresql/data so the existing
cluster on the volume is upgraded in place rather than re-initialised.
Drops the db_entrypoint config and DB_ENTRYPOINT_VERSION.

compose.yml

@@ -35,21 +35,22 @@ services:
         - "traefik.http.routers.${STACK_NAME}.tls.certresolver=${LETS_ENCRYPT_ENV}"
         - coop-cloud.${STACK_NAME}.version=4.0.0+v2.0.0
   db:
-    image: postgres:14.18
-    configs:
-      - source: db_entrypoint
-        target: /docker-entrypoint.sh
-        mode: 0555
-    # Custom docker entrypoint to handle major Postgres version upgrades
+    image: pgautoupgrade/pgautoupgrade:18-alpine
     volumes:
       - db-data:/var/lib/postgresql/data
-    entrypoint: /docker-entrypoint.sh
     environment:
+      # pin legacy PGDATA so the existing cluster on the volume is upgraded in place, not re-init'd
+      - PGDATA=/var/lib/postgresql/data
       - POSTGRES_USER=plausible
       - POSTGRES_PASSWORD=plausible
       - POSTGRES_DB=plausible
     networks:
       - internal
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U plausible -d plausible"]
+      interval: 5s
+      timeout: 5s
+      retries: 60
     deploy:
       labels:
         backupbot.backup: "true"
@@ -99,10 +100,6 @@ configs:
   clickhouse-user-config:
     name: ${STACK_NAME}_clickhouse_user_config_${CLICKHOUSE_USER_CONF_VERSION}
     file: clickhouse-user-config.xml
-  db_entrypoint:
-    name: ${STACK_NAME}_db_entrypoint_${DB_ENTRYPOINT_VERSION}
-    file: entrypoint.postgres.sh.tmpl
-    template_driver: golang
   clickhouse_entrypoint:
     name: ${STACK_NAME}_clickhouse_entrypoint_${CLICKHOUSE_ENTRYPOINT_VERSION}
     file: entrypoint.clickhouse.sh