Speed up ban list page load times with indexing.

[geominorai]

Description

Added two indices to the {prefix}_bans table and split the subquery for the ban history count into two on the ban list page.

Motivation and Context

Current ban history count subquery does not scale with a large number of rows in {prefix}_bans table and stalls ban list page load.

How Has This Been Tested?

Environment: Linux server running Apache with PHP 7.2 + MySQL 5.7.27

Load times on the ban list page while having 3.6k total bans have now been reduced from around 13 seconds to 1.
Please advise on the version number bump and updater file changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.

[geominorai]

Additional info from experiments:

• Adding a single index containing the three columns while keeping the query as-is had no effect on the page load time.
• Neither did adding a separate index for each of the three columns.