Add new indexes to locations and users for faster manager lookups

[uberbrady]

In many of our User lookups, we also return counts of "managed locations" and "managed users".

But unfortunately, we don't have indexes on manager_id for either of those, which can improve the performance of those subqueries.

This adds those two indexes

[what-the-diff]

PR Summary

• Database Optimization
  A new setup file has been added to improve data search in the 'locations' and 'users' tables in our database. The enhancement is centred around the 'manager_id' column in these tables.

• Index Creation
  We introduced a function (up() method) that will be used for creating these improvements. This operation acts to speed up the search of data in our database.

• Rollback Mechanism
  In case of any issues or a need to revert the changes, we have added a function (down() method) that unapplies these improvements. This safeguard ensures we can easily return to the previous state if necessary.