feat: optimize Spanner changestream metadata table

[thiagotnunes]

Adds indexes to the SpannerIO change streams metadata table. This serves to optimize two specific queries:

1. getUnfinishedMinWatermark
2. getAllPartitionsCreatedAfter

(micro-)Benchmarking results with a metadata table containing 11 million rows:

Method	No Indexes (current)	Index (this PR)
getUnfinishedMinWatermark	3.190s (+/- 0.91s)	0.020s (+/- 0.002s)
getAllPartitionsCreatedAfter	1.250s (+/- 0.230s)	0.012s (+/- 0.001s)

Customers can add these index manually if they want to by running the following DDL statements:

-- For GoogleSQL dialect
CREATE INDEX WatermarkIndex ON <Metadata Table Name> (Watermark) STORING (State);
CREATE INDEX CreatedAtStartTimestampIndex ON <Metadata Table Name> (CreatedAt, StartTimestamp);

-- For PostgreSQL dialect
CREATE INDEX "WatermarkIndex" ON <Metadata Table Name> ("Watermark") INCLUDE ("State");
CREATE INDEX "CreatedAtStartTimestampIndex" ON <Metadata Table Name> ("CreatedAt", "StartTimestamp");

[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

[thiagotnunes]

Run Java_GCP_IO_Direct PreCommit

[thiagotnunes]

assign set of reviewers

[github-actions]

Assigning reviewers. If you would like to opt out of this review, comment assign to next reviewer:

R: @robertwb for label java.
R: @Abacn for label io.
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)

The PR bot will only process comments in the main thread (not review comments).

[github-actions]

Reviewers are already assigned to this PR: @robertwb @Abacn @nielm

[Abacn]

LGTM, From the benchmark it sounds a great optimization!

[velamkao]

Hi @thiagotnunes would you know if this change to add the index is going to be part of Beam 2.59.0 release?

[velamkao]

feat: index creation toga4/spream#106

Never mind, I can see its there https://github.com/apache/beam/blob/v2.59.0-RC1/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/changestreams/dao/PartitionMetadataAdminDao.java