Bigtable: add a withColumns option on Bigtable reader

[mutianf]

A convenient way to include Bigtable columns in the Reader. This would be useful in templates since we can't pass in a RowFilter object in the template.

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Summary of Changes

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This pull request enhances the Bigtable reader by introducing a new withColumns option. This provides a convenient and templatable way to specify column filters for data retrieval, allowing users to define column families and qualifiers using a string-based format. This is especially beneficial in contexts like templates where direct RowFilter objects cannot be easily passed.

Highlights

• New withColumns Option: A withColumns method was added to BigtableIO.Read, allowing users to specify column filters using a flexible string format, which is particularly useful for templated pipelines.
• Flexible Column Specification: The new option supports a string format for defining column filters, including wildcards (*), explicit inclusions ({q1|q2}), and exclusions (!{q1|q2}) of qualifiers, with support for escaping special characters like comma and pipe.
• Chained Filtering Logic: The column filter generated from withColumns is automatically combined (chained) with any existing RowFilter specified via withRowFilter, enabling complex filtering scenarios.
• Internal Parsing and RowFilter Generation: New internal methods (parseColumns, addExcludeQualifiers, addIncludeQualifiers, cleanupQualifier) were implemented to convert the string-based column specification into a Bigtable RowFilter object.

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Changelog

• sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableIO.java
  • Added withColumns method to BigtableIO.Read for string-based column filtering.
  • Introduced COLUMN_REGEX and QUALIFIER_REGEX patterns for parsing column specifications.
  • Implemented parseColumns, addExcludeQualifiers, addIncludeQualifiers, and cleanupQualifier methods to construct RowFilter from column strings.
  • Modified getRowFilter to combine the new column filter with any existing row filter.
  • Added necessary imports for ColumnRange, TreeSet, Matcher, Pattern, Splitter, and ByteStringComparator.
• sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableReadOptions.java
  • Added getColumns() and setColumns() abstract methods to BigtableReadOptions and its Builder to store the column specification string.
  • Updated populateDisplayData to include the new columns option in display data.
  • Added validation for the columns option in the validate method.
• sdks/java/io/google-cloud-platform/src/test/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableIOTest.java
  • Added testParseColumnFilter to verify the parsing logic and RowFilter generation for various column string formats, including combined row and column filters.
  • Imported ColumnRange for testing column range filters.
  • Updated an existing test case to pass RowFilter directly to withRowFilter.

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