docs(samples): Dataflow to Apache Iceberg with dynamic destinations

[VeronicaWasson]

Description

Add snippet for Iceberg dynamic destinations

• Add a snippet that shows the use of [https://github.com/[Task]: Add utilities to easily implement portable dynamic destinations apache/beam#32365](dynamic destinations) when writing to Apache Iceberg from Dataflow, This is a new feature in Beam 2.60.

• Refactor integration tests to remove the assumption of exactly 1 destination table.

Relevant doc bug: b/371047621

Checklist

• I have followed Sample Format Guide
• pom.xml parent set to latest shared-configuration
• Appropriate changes to README are included in PR
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• Tests pass: mvn clean verify required
• Lint passes: mvn -P lint checkstyle:check required
• Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• dataflow/snippets/src/main/java/com/example/dataflow/ApacheIcebergDynamicDestinations.java:19, tag dataflow_apache_iceberg_dynamic_destinations
• dataflow/snippets/src/main/java/com/example/dataflow/ApacheIcebergDynamicDestinations.java:72, tag dataflow_apache_iceberg_dynamic_destinations

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment