Add WithNoOutputTimestamp to go sdk matching Java SDK.

[scwhittle]

Add integration tests of WithOutputTimestamp and WithNoOutputTimestamp

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[gemini-code-assist]

Summary of Changes

Hello @scwhittle, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Apache Beam Go SDK by adding a WithNoOutputTimestamp option for timers. This new option provides more control over watermark progression by allowing timers to fire without explicitly setting an output timestamp, ensuring that elements emitted from such timers default to MaxTimestamp. The change is supported by new integration tests that verify the correct behavior of timers with and without explicit output timestamps, ensuring consistency and reliability.

Highlights

• New Timer Option: Introduced WithNoOutputTimestamp to the Go SDK's timer functionality, allowing timers to be set without holding up the output watermark, aligning with the Java SDK's capabilities.
• Integration Tests: Added comprehensive integration tests to validate the behavior of both WithOutputTimestamp and the newly added WithNoOutputTimestamp for event time timers.

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[github-actions]

Assigning reviewers:

R: @lostluck for label go.

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[lostluck]

Run Go PostCommit

[lostluck]

If that comment doesn't work, touch .github/trigger_files/beam_PostCommit_Go.json and add it to the PR.

Per https://github.com/apache/beam/tree/master/.github/workflows#postcommit-jobs

The PR passes against Prism, which is a decent sign, but for timers, it's best to validate against Dataflow just in case.

[lostluck]

LGTM other than checking against Dataflow.

[scwhittle]

Thanks! I added the trigger file and the tests are passing so merging.