fix(svc-db-postgres): pin Postgres version to 17-3.5, add entity_name var, and dynamically resolve major version for dev package

- Changed default Docker image version from 'latest' to '17-3.5' in config
- Introduced entity_name var for consistent lookups
- Added POSTGRES_VERSION and POSTGRES_VERSION_MAJOR extraction
- Updated Dockerfile to install postgresql-server-dev-<major> with default fallback to 'all'
- Minor YAML formatting improvements

Ref: https://chatgpt.com/share/68de40b4-2eb8-800f-ab5b-11cc873c3604

roles/svc-db-postgres/config/main.yml

@@ -6,7 +6,7 @@ docker:
       name:               postgres
       # Please set an version in your inventory file! 
       # Rolling release isn't recommended
-      version:            "latest"
+      version:            "17-3.5"
       backup:
         database_routine: true
       cpus:               "2.0"
@@ -14,5 +14,5 @@ docker:
       mem_limit:          "6g"
       pids_limit:         1024
   volumes:
-    data:     "postgres_data"
-  network:    "postgres"
+    data:                 "postgres_data"
+  network:                "postgres"