add support for bigtable materialized view source

[psud]

Adds support in the BigTable IO Java connector for BigTables new materialized views. Fixes #38053

• Adds BigtableIO.read().withMaterializedViewName() as an alternative to withTableId() for reading from Bigtable Continuous Materialized Views
• Uses the client library's MaterializedViewId / TargetId APIs for correct resource path construction
• Reuses all the existing logic and plumbing from table reads as materialized view reads use almost all the same concepts
• Updates schema transform provider, validation, and both reader implementations

Testing

• Tested against a real BigTable materialized view (manual testing outside of this repo)
• Unit tests for builder, mutual exclusivity validation, and both reader implementations with MV name

---

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• Update CHANGES.md with noteworthy changes.
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[gemini-code-assist]

Summary of Changes

Hello, 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 introduces support for reading from Bigtable Continuous Materialized Views within the Bigtable IO Java connector. It provides a new configuration option that is mutually exclusive with the existing table ID parameter, updates the underlying service implementation to correctly construct resource paths for materialized views, and includes necessary validation and testing to ensure robust integration.

Highlights

• New Feature: Added support for reading from Bigtable Continuous Materialized Views using BigtableIO.read().withMaterializedViewName().
• API Changes: Updated BigtableIO, BigtableReadOptions, and SchemaTransformProvider to support materialized views, ensuring mutual exclusivity with standard table IDs.
• Internal Implementation: Updated BigtableServiceImpl to use MaterializedViewId for resource path construction and updated validation logic to handle materialized views.
• Testing: Added comprehensive unit tests in BigtableIOTest and BigtableServiceImplTest to verify materialized view reading and validation logic.

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[psud]

R: @kennknowles or R: @tonytanger as you two are the most frequent commiters on the BigTableIO.java file

Would you be able to take a look at this PR, please? It uses all the same mechanisms that the normal BigTable source uses to read from tables but adds options and usage of the materialized views endpoints. Please also let me know if this doesn't qualify as a "small" PR and I should send out an email to dev@beam.apache.org to discuss this

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[psud]

R: @tonytanger