Improve user search performance

# Problem

When querying a lot of users from Authgear, e.g. for a user sync job, the resources usage on the DB is very high.

## Solution

Reduce complexity by not encoding pagination in the cursor by default

Start by tracing Authgear’s user search query and cursor pagination implementation, then measure database resource use during a large user sync. Done means pagination is no longer encoded in the cursor by default and large user queries use fewer database resources.

Written by the indexing model from the issue text.