[CAPT-1614] Refactors admin task pagination

[asmega]

Context

• https://dfedigital.atlassian.net/browse/CAPT-1614
• Does not directly link to this ticket but refactors admin task pagination so it becomes much easier to change

Changes

• Extracts admin task pagination from an inherited controller concern to a PORO which is more self contained
• This allows for later work to be able to manipulate pagination without needing to deal with rails controllers
• The later work to comes becomes more complex as we will no longer simply be paginating between tasks but also decisions. Due to historical decisions where by we seem to have concepts of decisions and tasks but user experience needs to treat them as if a single entity