feat(replication): map HBase table names to Cloud Bigtable table IDs

[vermas2012]

Support mapping HBase table names (such as namespaced tables like my_namespace:my_table) to valid Cloud Bigtable table IDs during live WAL replication via three mutually exclusive configuration mechanisms:

• google.bigtable.replication.table_name_mapping: inline JSON object (identical format to HBaseSchemaTranslator's google.bigtable.schema.mapping.filepath)
• google.bigtable.replication.table_name_mapping_file: JSON file path resolved via Hadoop FileSystem (with local filesystem fallback when URI scheme is omitted)
• google.bigtable.replication.table_name_mapping.<hbase_table>: direct per-table properties in hbase-site.xml or peer configuration

Key Details

• Enforces 1:1 injectivity across canonicalized HBase source tables (e.g. default:t and t) and target Cloud Bigtable table IDs (including unmapped identity fallback collision detection).
• Coalesces WAL entries by mapped target table prior to row-key grouping to preserve per-row mutation ordering.
• Hardens JSON token validation, bounded file streaming, bidirectional marker detection, and batch threshold checks.

[gemini-code-assist]

Code Review

This pull request introduces a mechanism to map HBase table names to Cloud Bigtable table IDs, which is particularly useful for handling HBase tables in non-default namespaces. The changes include a new TableNameMapper class to handle these mappings via inline JSON, external files, or prefixed configuration properties, and updates to CloudBigtableReplicator to apply these mappings during replication. Additionally, the PR includes robust error handling for mapping collisions, improved batching logic for replication tasks, and comprehensive unit tests to verify the new functionality.