Enhance GetETagPropertyName method to handle ETag lookup in both entity and base types

[rezaghadimim]

Enhance GetETagPropertyName method to handle ETag lookup in both entity and base types

• Added test to cover this scenario and ensure proper functionality

Fixes #35336

Please check whether the PR fulfills these requirements

• I've read the guidelines for contributing and seen the walkthrough
• I've posted a comment on an issue with a detailed description of how I am planning to contribute and got approval from a member of the team
• The code builds and tests pass locally (also verified by our automated build checks)
• Commit messages follow this format:

        Summary of the changes
        - Detail 1
        - Detail 2

        Fixes #bugnumber

• Tests for the changes have been added (for bug fixes / features)
• Code follows the same patterns and style as existing code in this repo

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[SamMonoRT]

@rezaghadimim - the test failures seem related

[rezaghadimim]

@rezaghadimim - the test failures seem related

Please run it again as I don't think the error is related to the code. If possible, run the second issue again too. I've seen the following errors:
Wait-CosmosDbEmulator: The emulator failed to reach Running status within 360 seconds

[AndriySvyryd]

Thanks for your contribution!