docs: Add samples and tests for ingestion from Kafka sources

[michaelpri10]

CPS Kafka ingestion samples

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/snippets/src/main/java/pubsub/CreateTopicWithAwsMskIngestionExample.java:19, tag pubsub_create_topic_with_aws_msk_ingestion
• samples/snippets/src/main/java/pubsub/CreateTopicWithAzureEventHubsIngestionExample.java:19, tag pubsub_create_topic_with_azure_event_hubs_ingestion
• samples/snippets/src/main/java/pubsub/CreateTopicWithConfluentCloudIngestionExample.java:19, tag pubsub_create_topic_with_confluent_cloud_ingestion

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