docs(samples): add samples and tests for change streams transaction exclusion

[ShuranZhang]

Add samples and IT tests on setting Options.excludeTxnFromChangeStreams() in various write requests. This is a follow up after #2959

[snippet-bot]

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• samples/snippets/src/main/java/com/example/spanner/ChangeStreamsTxnExclusionSample.java:55, tag spanner_set_exclude_txn_from_change_streams

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[ShuranZhang]

Hi @rahul2393 Could you please take a look at this pr? This is a Java version of GoogleCloudPlatform/golang-samples#4108 for code samples using change streams transaction exclusion. The newest BOM release now contains the needed source code change so this pull request should be ready to merge. Thank you!

[rahul2393]

LGTM, with some nits on project/instance naming