Advanced User Search

Implement advanced search for users. Currently user search performs a basic (database) search but this has performance issues and doesn't leverage the capabilities of elasticsearch.

Steps:

• Create a user index
• Perform a callback on user to update elasticsearch
• Create a migration to backfill users
• Implement advanced user search
• Enable the advanced_user_search feature flag
• Remove the feature flag

Release notes

User Search is now supported by Advanced Search. This not only improves the User Search performance but also gives the ability to refine the search using Advanced Search Syntax.