[FLINK-38355][table][FLIP-546] Support CREATE OR ALTER MATERIALIZED TABLE syntax

[raminqaf]

What is the purpose of the change

This pull request implements the CREATE OR ALTER MATERIALIZED TABLE syntax as proposed in FLIP-546. This new command provides an idempotent way to manage materialized tables, enabling declarative deployment patterns for CI/CD pipelines and infrastructure-as-code workflows.

The command intelligently routes to either CREATE or ALTER logic:

• If the materialized table does not exist, it creates a new table (behaves like CREATE MATERIALIZED TABLE)
• If the materialized table already exists, it modifies the query definition (behaves like ALTER MATERIALIZED TABLE AS)

This eliminates the need for complex DROP-IF-EXISTS patterns and makes materialized table management more robust and predictable in automated deployment scenarios.

Brief change log

• Added CREATE OR ALTER MATERIALIZED TABLE SQL syntax to the Flink SQL parser
• Extended SqlCreateOrAlterMaterializedTable to handle both create and alter operations based on table existence
• Refactored materialized table parsing and building logic into SqlCreateOrAlterMaterializedTableConverter for better encapsulation
• Added getOriginalQuery() method to CatalogMaterializedTable interface (aligning with CatalogView interface)
• Added comprehensive tests for CREATE OR ALTER behavior in both create and alter scenarios
• Updated documentation to include CREATE OR ALTER MATERIALIZED TABLE syntax and examples

Verifying this change

This change added tests and can be verified as follows:

• Added unit tests in MaterializedTableStatementParserTest to verify SQL parsing of CREATE OR ALTER syntax
• Added integration tests in SqlMaterializedTableNodeToOperationConverterTest:
  • testCreateOrAlterMaterializedTable() - verifies CREATE behavior when table doesn't exist
  • testCreateOrAlterMaterializedTableForExistingTable() - verifies ALTER behavior when table exists with schema evolution
• Extended integration tests in SqlGatewayRestEndpointMaterializedTableITCase to validate end-to-end behavior via REST API
• Verified that existing CREATE and ALTER tests continue to pass, ensuring backward compatibility
• Manually verified idempotent behavior by running the same CREATE OR ALTER statement multiple times

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): yes - CatalogMaterializedTable interface extended with getOriginalQuery() method
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? docs - Added new section in docs/content/docs/dev/table/materialized-table/statements.md explaining CREATE OR ALTER syntax, behavior, examples, and use cases

[flinkbot]

CI report:

• 3033271 UNKNOWN
• d5640aa Azure: SUCCESS

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• @flinkbot run azure re-run the last Azure build

[snuyanzin]

ideally this method should be in alterMaterializedTable converter
may be we can move it in future when that converter becomes more mature

[raminqaf]

I think it is better if we move it later with the corresponding PR.