Migrate consultation's assigned_to to assigned_clinicians

[Ashesh3]

Requires: https://github.com/coronasafe/care/pull/1900 This pull request migrates the assigned_to field in the consultation model to assigned_clinicians. This change is made to improve clarity and consistency in the codebase.

Phases for the change

1. Schema Changes
2. Migrating Data and Deprecating assigned_to

Related Issue: https://github.com/coronasafe/care_fe/issues/6276