feat: add SQL codes for PgUser (3D027, 42P020)

- Add SQL_STATE_INVALID_PG_USER (3D027) for invalid PG user errors
- Add SQL_STATE_DUPLICATE_PG_USER (42P020) for duplicate PG user errors
- Aligns with deltastreamv2 go-utils/errors/sqlcode.go

Author: kraman

src/deltastream/api/error.py

@@ -105,6 +105,7 @@ class SqlState(str, Enum):
     SQL_STATE_3D024 = "3D024"
     SQL_STATE_3D025 = "3D025"
     SQL_STATE_3D026 = "3D026"
+    SQL_STATE_3D027 = "3D027"
     SQL_STATE_42P09 = "42P09"
     SQL_STATE_42P10 = "42P010"
     SQL_STATE_42P11 = "42P011"
@@ -116,6 +117,7 @@ class SqlState(str, Enum):
     SQL_STATE_42P17 = "42P017"
     SQL_STATE_42P18 = "42P018"
     SQL_STATE_42P19 = "42P019"
+    SQL_STATE_42P20 = "42P020"
 
     # Class 00 — Successful Completion
     SQL_STATE_SUCCESSFUL_COMPLETION = SQL_STATE_00000
@@ -171,6 +173,7 @@ class SqlState(str, Enum):
     SQL_STATE_INVALID_USERDATA = SQL_STATE_3D024
     SQL_STATE_INVALID_DATAPLANE = SQL_STATE_3D025
     SQL_STATE_INVALID_PLAYBOOK = SQL_STATE_3D026
+    SQL_STATE_INVALID_PG_USER = SQL_STATE_3D027
 
     # Class 3E — Resource not ready
     SQL_STATE_STORE_NOT_READY = SQL_STATE_3E001
@@ -199,6 +202,7 @@ class SqlState(str, Enum):
     SQL_STATE_DUPLICATE_RELATION = SQL_STATE_42P17
     SQL_STATE_DUPLICATE_SCHEMA_REGISTRY = SQL_STATE_42P18
     SQL_STATE_DUPLICATE_COMPUTE_POOL = SQL_STATE_42P19
+    SQL_STATE_DUPLICATE_PG_USER = SQL_STATE_42P20
     SQL_STATE_AMBIGUOUS_ORGANIZATION = SQL_STATE_42P001
     SQL_STATE_AMBIGUOUS_STORE = SQL_STATE_42P002