Add filter to GetMinUnfinishedWatermark queryAdd filter tester

[changliiu]

To improve the performance of the query for GetUnfinishedMinWatermark, we can add a filter to the query.
Note that the query run on a cache to refresh every 1s. We can remember the cached value every time and use the value as a filter in the next time query.

Also add class level timeout for all change stream integration tests.

Note that, the CacheLoader's refresh function cannot return null, because that will be deemed invalid, then the cache will not be updated. As the result, the connector will run forever. Hence we still keep the return type optional.

[changliiu]

Integration test can pass locally https://screenshot.googleplex.com/6aQBPAW8YT69VTd

[github-actions]

Checks are failing. Will not request review until checks are succeeding. If you'd like to override that behavior, comment assign set of reviewers

[changliiu]

Run integration test locally based on earlier commit #34883 and it passed. Hence the integration timeout is not caused by this PR.

[changliiu]

assign set of reviewers

[github-actions]

Assigning reviewers:

R: @m-trieu for label java.
R: @nielm for label spanner.

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[github-actions]

Reminder, please take a look at this pr: @m-trieu @nielm

[github-actions]

Assigning new set of reviewers because Pr has gone too long without review. If you would like to opt out of this review, comment assign to next reviewer:

R: @chamikaramj for label java.
R: @nielm for label spanner.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

[changliiu]

Friendly ping :)

[changliiu]

Friendly ping :)

[changliiu]

Friendly ping :)

[Abacn]

It seems GCP IO integration test stucks indefinitely. Retriggered the test

update: second try still stuck, retriggering

If it timeouts for the third time, consider add class level test timeout for integraton tests that might be affected to debug