Feature/add total results

[euanwm]

Major breaking change to the leaderboard API endpoint to allow for the total amount of lifters to be known in a filter query.

Schema:

{
    "size": int,
    "data": [{lift_data_1}, {lift_data_2}, {lift_data_etc}],
}

[euanwm]

@mountclear / @rsbrowne - It is done.

[codecov[bot]]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (9eb8a32) 91.11% compared to head (8c98c3f) 87.27%.

Files	Patch %	Lines
backend/dbtools/sortby.go	40.42%	26 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #270 +/- ## =============================================== - Coverage 91.11% 87.27% -3.84% =============================================== Files 11 12 +1 Lines 360 393 +33 =============================================== + Hits 328 343 +15 - Misses 25 42 +17 - Partials 7 8 +1 ```

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