fix(ingest/pulsar): handle Avro schema with missing namespace or name

[Alice-608]

fix: pulsar ingestion fails when Avro schema is missing namespace or name

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[Alice-608]

fix: pulsar ingestion fails when Avro schema is missing namespace or name

Problem Description
During the Pulsar ingestion process in DataHub, if the Avro schema for a topic is missing either the namespace or name field, the ingestion process crashes with the following error:
<class 'TypeError'>: unsupported operand type(s) for +: 'NoneType' and 'str'

The root cause is that the code attempts to concatenate these fields without checking if they exist:
self.schema_name = avro_schema.get("namespace") + "." + avro_schema.get("name")

Fix Description
This fix introduces the following changes:
Validation: Check for the presence of the namespace and name fields before concatenation.
Default Values: If either field is missing, assign default values:
namespace: "default_namespace"
name: "default_name"
Informational Logging: Log messages to inform users about missing fields and the default values used.
This ensures that the ingestion process no longer fails due to missing schema fields and continues processing metadata gracefully.

Modified Files
datahub/metadata-ingestion/src/datahub/ingestion/source/pulsar.py

[shirshanka]

Changes look good - I accepted @sgomezvillamor's suggestion

[sgomezvillamor]

The latest build failed because of a format issue, which should be fixed with:

Suggested change

	avro_schema.get("namespace") + "." + avro_schema.get("name")
	avro_schema.get("namespace") + "." + avro_schema.get("name")