Database: Order results in UserSearch by username/email

[aknuds1]

What this PR does / why we need it:
Ensure that the user list on the admin page is ordered by username first and email address second.

Also adding an index on (user.login, user.email) for speedy ordering.

I've checked with MariaDB (MySQL compatible) and it looks as if the new index gets used:

MariaDB [grafana]> explain select id, login,email from user order by login ASC, email ASC\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: user
         type: index
possible_keys: NULL
          key: IDX_user_login_email
      key_len: 1524
          ref: NULL
         rows: 1
        Extra: Using index
1 row in set (0.000 sec)

Which issue(s) this PR fixes:
Fixes #22348.

[kylebrandt]

Have you done a describe on say at least mysql to make sure we not changing the performance characteristics (e.g. index needed?).

[aknuds1]

@kylebrandt Good point! I included you as a reviewer for a reason ;)

[aknuds1]

@kylebrandt Index is added now.

[marefr]

Great. LGTM