Common: Support postgreSQL database as the metadata db. (#2357)

https://github.com/infiniflow/ragflow/issues/2356

### What problem does this PR solve?

As title

### Type of change

- [X] New Feature (non-breaking change which adds functionality)

conf/service_conf.yaml

@@ -9,6 +9,14 @@ mysql:
   port: 3306
   max_connections: 100
   stale_timeout: 30
+postgres:
+  name: 'rag_flow'
+  user: 'rag_flow'
+  password: 'infini_rag_flow'
+  host: 'postgres'
+  port: 5432
+  max_connections: 100
+  stale_timeout: 30
 minio:
   user: 'rag_flow'
   password: 'infini_rag_flow'