FinishPartitionWatchDog consuming high CPU [DBZ-6230]

Migrated from [DBZ-6230](https://issues.redhat.com/browse/DBZ-6230)

h2. What Debezium connector do you use and what version?

v2.2.0.Alpha1
h2. What is the connector configuration?

{"name": "livestream-connector","config":

{ "connector.class": "io.debezium.connector.spanner.SpannerConnector", "tasks.max": "1", "gcp.spanner.change.stream": "live-table", "gcp.spanner.project.id": "project-stag, "gcp.spanner.instance.id": "development-instance", "gcp.spanner.database.id": "live-db", "gcp.spanner.credentials.path": "/app/services-sa.json", "key.converter.schemas.enable":false, "value.converter.schemas.enable":false }

}
h2. What is the captured database version and mode of deployment?

GCP Managed Spanner DB and Kafka connect deployed on K8s.
h2. What behaviour do you expect?

Less CPU usage.
h2. What behaviour do you see?

High CPU usage. Related [thread|https://debezium.zulipchat.com/#narrow/stream/302529-users/topic/High.20CPU.20consumption.20in.20Spanner.20debezium] on zulip.

!https://issues.redhat.com/secure/temporaryattachment/1232fddd0af50208bb83185b550701cdba5e52c8/temp4978268862975678595_image-2023-03-19-11-21-01-268.png|width=919,height=493!
h2. Do you see the same behaviour using the latest relesead Debezium version?

Yes.
h2. Do you have the connector logs, ideally from start till finish?

Yes.
h2. How to reproduce the issue using our [tutorial|https://github.com/debezium/debezium-examples/tree/main/tutorial] deployment?

Reproducible with normal config.
h1. Feature request or enhancement
h2. Which use case/requirement will be addressed by the proposed feature?

Less CPU usage
h2. Implementation ideas (optional)

Increase sleep time or subscribe to finishedPartition changes rather than polling it [here|https://github.com/debezium/debezium-connector-spanner/blob/ed4fe34fe887e9f5304a40d6d74b2bdf2879f06a/src/main/java/io/debezium/connector/spanner/FinishPartitionWatchDog.java#L35].

Start with src/main/java/io/debezium/connector/spanner/FinishPartitionWatchDog.java, especially the polling logic at the linked line. Reproduce the high CPU behavior with the normal Spanner connector configuration and compare CPU usage while checking that finished-partition handling still works. Done means materially lower CPU usage without losing watchdog behavior.

Written by the indexing model from the issue text.