[Dashboard] Support leaderboard sorting by reputation and fee on BE

[dnechay]

Description
Right now leaderboard table fetches pre-ordered data (sorted by stake amount) from BE, displays all the results and allows to sort them by different columns, but this sorting is done fully on UI, so it might not meet user expectations. Instead when user initiates sorting of the table by column other than "Stake" - we should make a request to BE to get leaders sorted by new criteria, not sort an existing list.

Motivation
In order to allow users to see leaders sorted by different criteria.

Implementation details
TBD by developer