add "azure-asyncoperation" header into mgmt-core

[xiangyan99]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

If an SDK is being regenerated based on a new API spec, a link to the pull request containing these API spec changes should be included above.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

This PR adds support for the azure-asyncoperation header in ARM polling continuation tokens by overriding the _filter_headers_for_continuation_token method in both ARMPolling and AsyncARMPolling classes. The changes update the minimum azure-core version to 1.38.0 to use the new continuation token infrastructure.

Changes:

• Updated azure-core dependency from >=1.32.0 to >=1.38.0
• Added _filter_headers_for_continuation_token override in ARMPolling and AsyncARMPolling classes
• Created new _utils.py module with _filter_arm_headers function

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sdk/core/azure-mgmt-core/setup.py	Bumped azure-core minimum version to 1.38.0 to support new continuation token format
sdk/core/azure-mgmt-core/azure/mgmt/core/polling/arm_polling.py	Added _filter_headers_for_continuation_token override and imported _filter_arm_headers utility
sdk/core/azure-mgmt-core/azure/mgmt/core/polling/async_arm_polling.py	Added _filter_headers_for_continuation_token override for async polling
sdk/core/azure-mgmt-core/azure/mgmt/core/polling/_utils.py	Created new utility module with ARM-specific header filtering logic
sdk/core/azure-mgmt-core/CHANGELOG.md	Added changelog entry documenting the bug fix