feat: add support for Proto columns

[harshachinta]

This PR adds support for Proto Columns

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 4 region tags.

• samples/proto-query-data.js:26, tag spanner_query_with_proto_types_parameter
• samples/proto-type-add-column.js:29, tag spanner_add_proto_type_columns
• samples/proto-update-data-dml.js:26, tag spanner_update_data_with_proto_types_with_dml
• samples/proto-update-data.js:26, tag spanner_update_data_with_proto_types

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[generated-files-bot[bot]]

Warning: This pull request is touching the following templated files:

• README.md - README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml
• samples/README.md - samples/README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml