Support FIREBASE_TENANT_EMULATOR_HOST in TenantManagementService

[KetanHegde]

Summary

This PR adds support for running TenantManagementService against the Firebase Authentication Emulator using a new environment variable, FIREBASE_TENANT_EMULATOR_HOST.

When this environment variable is set, _TenantManagementService uses the emulator endpoint instead of the production Identity Toolkit endpoint and initializes the client with EmulatorAdminCredentials.

Changes

• Added support for FIREBASE_TENANT_EMULATOR_HOST
• Added get_tenant_emulator_host() helper
• Updated _TenantManagementService to use the emulator endpoint when configured
• Added unit tests covering emulator behavior for tenant management
• Updated existing tenant management tests to support both production and emulator endpoints

Testing

Executed:

pytest tests/test_tenant_mgt.py

Result:

311 passed

Also verified with:

pylint firebase_admin tests/test_tenant_mgt

The remaining pylint warnings are pre-existing in the test module.

Implements #910

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[gemini-code-assist]

Code Review

This pull request introduces support for the Firebase Tenant Emulator by checking the FIREBASE_TENANT_EMULATOR_HOST environment variable and configuring the tenant management service to use the emulator host and credentials when available. The tests have also been updated to run in both emulated and non-emulated modes. Feedback on this PR suggests falling back to the standard FIREBASE_AUTH_EMULATOR_HOST if the tenant-specific emulator host is not set, ensuring a smoother developer experience when running the local Auth emulator.