[Identity] Prepare beta release

[pvaneck]

• Update changelog + version.
• Readd token binding feature that was removed in [Identity] Prepare release #45112.

[Copilot]

Pull request overview

Prepares azure-identity for the 1.26.0b2 beta release and reintroduces WorkloadIdentityCredential’s AKS identity binding (token proxy) support, including new transports and expanded test coverage.

Changes:

• Re-add token proxy support to WorkloadIdentityCredential (sync + async) via new token-binding transport implementations.
• Add extensive unit/integration tests covering proxy endpoint rewriting, SNI, and CA rotation handling.
• Update release metadata/docs: bump version + changelog entry + troubleshooting guidance.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
sdk/identity/azure-identity/tests/test_workload_identity_credential_async.py	Adds async tests for token proxy transports, SNI/CA handling, and local-server integration coverage.
sdk/identity/azure-identity/tests/test_workload_identity_credential.py	Adds sync tests for token proxy transports and local-server integration coverage.
sdk/identity/azure-identity/pyproject.toml	Updates package classifier for the beta release.
sdk/identity/azure-identity/azure/identity/aio/_internal/token_binding_transport_asyncio.py	Adds async fallback transport based on AsyncioRequestsTransport.
sdk/identity/azure-identity/azure/identity/aio/_internal/token_binding_transport_aiohttp.py	Adds aiohttp-based custom transport with SNI + CA support.
sdk/identity/azure-identity/azure/identity/aio/_credentials/workload_identity.py	Wires enable_azure_proxy into async WorkloadIdentityCredential and adds transport selection logic.
sdk/identity/azure-identity/azure/identity/_version.py	Bumps version to 1.26.0b2.
sdk/identity/azure-identity/azure/identity/_internal/token_binding_transport_requests.py	Adds sync requests-based custom transport with SNI + CA support.
sdk/identity/azure-identity/azure/identity/_internal/token_binding_transport_mixin.py	Adds shared mixin for proxy URL rewriting + CA file tracking/validation.
sdk/identity/azure-identity/azure/identity/_credentials/workload_identity.py	Wires enable_azure_proxy into sync WorkloadIdentityCredential and adds transport creation helper.
sdk/identity/azure-identity/azure/identity/_constants.py	Adds new environment variable names for token proxy configuration.
sdk/identity/azure-identity/TROUBLESHOOTING.md	Adds troubleshooting entry for identity binding mode errors and mitigation.
sdk/identity/azure-identity/CHANGELOG.md	Adds 1.26.0b2 changelog entry documenting the breaking rename.

[pvaneck]

/check-enforcer override