fix(BA-1186): VFolder clone not working

[fregataa]

resolves #4212 (BA-1186)

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue

[Copilot]

Pull Request Overview

This PR fixes the issue with cloning VFolders by ensuring the correct user record and associated policies are retrieved. The changes include switching to a new method to fetch the user with policies in vfolder cloning and adding several query helper methods and type aliases in the user model.

• Changed user fetching in vfolder cloning to use get_user_by_id_with_policies.
• Updated retrieval of allowed vfolder hosts from the main keypair’s resource policy.
• Added new query helper functions, condition merging, and related fields support in the user model.

Reviewed Changes

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

File	Description
src/ai/backend/manager/services/vfolder/services/vfolder.py	Updates to ensure the correct user record with policies is fetched and to retrieve allowed hosts from main keypair.
src/ai/backend/manager/models/user.py	New query functions and type aliases for dynamic condition merging and related field loading.

Comments suppressed due to low confidence (1)

src/ai/backend/manager/models/user.py:319

• [nitpick] The inner function name '_by_userusername' in the by_username function is inconsistent with its purpose; consider renaming it to '_by_username' for clarity.

def _by_userusername(

[jopemachine]

Project vfolder cloning is still not working.