docs(metadata-models-custom): add example script to show producing cu… (datahub-project#4681)

Author: shirshanka

metadata-models-custom/README.md

@@ -129,6 +129,15 @@ results in
 Update succeeded with status 200
 ```
 
+The `scripts/insert_custom_aspect.py` script shows you how to accomplish the same using the Python SDK. Note that we are just using a raw dictionary here to represent the `dq_rule` aspect and not a strongly-typed class.
+```console
+cd scripts
+python3 insert_custom_aspect.py
+```
+results in
+```console
+Successfully wrote to DataHub
+```
 
 ## Advanced Guide
 

metadata-models-custom/scripts/insert_custom_aspect.py

@@ -0,0 +1,48 @@
+import json
+
+from datahub.emitter.rest_emitter import DatahubRestEmitter
+from datahub.metadata.schema_classes import (
+    ChangeTypeClass,
+    GenericAspectClass,
+    MetadataChangeProposalClass,
+)
+
+dq_aspect = {
+    "rules": [
+        {
+            "field": "my_event_data",
+            "isFieldLevel": False,
+            "type": "isNull",
+            "checkDefinition": "n/a",
+            "url": "https://github.com/datahub-project/datahub/blob/master/checks/nonNull.sql",
+        },
+        {
+            "field": "timestamp",
+            "isFieldLevel": True,
+            "type": "increasing",
+            "checkDefinition": "n/a",
+            "url": "https://github.com/datahub-project/datahub/blob/master/checks/increasing.sql",
+        },
+    ]
+}
+
+emitter: DatahubRestEmitter = DatahubRestEmitter(gms_server="http://localhost:8080")
+
+dataset_urn = "urn:li:dataset:(urn:li:dataPlatform:hive,logging_events,PROD)"
+mcp_raw: MetadataChangeProposalClass = MetadataChangeProposalClass(
+    entityType="dataset",
+    entityUrn=dataset_urn,
+    changeType=ChangeTypeClass.UPSERT,
+    aspectName="customDataQualityRules",
+    aspect=GenericAspectClass(
+        contentType="application/json",
+        value=json.dumps(dq_aspect).encode("utf-8"),
+    ),
+)
+
+try:
+    emitter.emit(mcp_raw)
+    print("Successfully wrote to DataHub")
+except Exception as e:
+    print("Failed to write to DataHub")
+    raise e