User administration + analytics designs

Created by: rrhyne

Users require the ability to view event data alongside the users they are managing. Transform the current administration page to use a table, present event data and be sortable and filterable to allow users to remove users by various criteria.

• Minimum required functionality
• Desired functionality.

Make it be enabled/disabled via feature flag.

Subtasks:

• https://github.com/sourcegraph/sourcegraph/issues/39820
  • https://github.com/sourcegraph/sourcegraph/pull/39926
  • https://github.com/sourcegraph/sourcegraph/pull/40077
  • https://github.com/sourcegraph/sourcegraph/pull/40123
  • https://github.com/sourcegraph/sourcegraph/pull/40301
• https://github.com/sourcegraph/sourcegraph/issues/39821
• https://github.com/sourcegraph/sourcegraph/pull/40339
• https://github.com/sourcegraph/sourcegraph/pull/40437