feat(postgres): complete sequence names in regclass literals

Closes #4005

agents/common/src/main/java/com/dbx/agent/CompletionAssistantCandidateKind.java

@@ -17,6 +17,8 @@ public enum CompletionAssistantCandidateKind {
     FUNCTION,
     @SerializedName("column")
     COLUMN,
+    @SerializedName("sequence")
+    SEQUENCE,
     @SerializedName("object")
     OBJECT
 }

agents/common/src/main/java/com/dbx/agent/CompletionAssistantObjectKind.java

@@ -18,5 +18,7 @@ public enum CompletionAssistantObjectKind {
     @SerializedName("function")
     FUNCTION,
     @SerializedName("column")
-    COLUMN
+    COLUMN,
+    @SerializedName("sequence")
+    SEQUENCE
 }