Docs: Add comment for IdentityResizer in image_resizer.proto

[rajonya-m]

Description

Summary

This PR adds documentation for the IdentityResizer message in the image_resizer.proto file under the Object Detection API.

Motivation and Context

The IdentityResizer option was previously undocumented, making it unclear what its function was in the image resizing configuration. This update clarifies that it performs no resizing and is appropriate for use cases where the input images are already preprocessed or when using models that support dynamic input sizes.

Dependencies

No new dependencies are introduced.

Type of change

Documentation update

Tests

Since this is a documentation-only change in a .proto file, no runtime tests were needed. The updated comments were manually reviewed in VS Code to ensure correct syntax and formatting.

Test Configuration:

Editor: Visual Studio Code

OS: Windows 10

Environment: Git Bash terminal

Validation: Manual .proto formatting and placement check

Checklist

I have signed the Contributor License Agreement.

I have read guidelines for pull request.

My code follows the coding guidelines.

I have performed a self code review of my own code.

I have commented my code, particularly in hard-to-understand areas.

I have made corresponding changes to the documentation.

My changes generate no new warnings.

[n/a] I have added tests that prove my fix is effective or that my feature works.

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[mihaimaruseac]

Why is this comment needed?

[rajonya-m]

I added this comment because IdentityResizer was previously undocumented in image_resizer.proto. For new users, it may not be obvious that this option is valid or what its purpose is. Documenting it clarifies that:
It performs no resizing.
It is appropriate when input images are already preprocessed.
It can be used with models that support dynamic input sizes.

[mihaimaruseac]

It is an empty proto. It does not need to be documented by itself.