feat: replace enterprise_support import with AccountSettingsReadOnlyFieldsRequested filter

[pwnage101]

Removes the direct import of get_enterprise_readonly_account_fields from openedx.features.enterprise_support.utils in accounts/api.py and replaces it with a call to the AccountSettingsReadOnlyFieldsRequested openedx-filter. Adds the filter to OPEN_EDX_FILTERS_CONFIG. Updates tests to mock the filter instead of the old enterprise_support imports.

ENT-11510

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

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Blocked by:

• feat: add AccountSettingsReadOnlyFieldsRequested filter openedx-filters#334
• feat: add AccountSettingsEnterpriseReadOnlyFieldsStep pipeline step edx-enterprise#2544

[pwnage101]

Some notes on requirements for platform:

• openedx/openedx-platform uses python 3.12 to run make upgrade, while edx/edx-platform (2U fork) uses 3.11. You need both python versions available to upgrade requirements for both separately.
• We added social-auth-app-django as a hard dependency on the edx-enterprise python package, so it makes sense that pip-tools wants to mark edx-enterprise as wanting it. Often you can fix this automatically using compile-requirements if you just want to limit what gets upgraded and fix the comments only:

# openedx/openedx-platform
pyenv local 3.12.13
make compile-requirements

# edx/edx-platform
pyenv local 3.11.14
make compile-requirements