Fixed #10052 - Added api endpoint for retrieving assets checked out to asset

[marcusmoore]

This PR populates a stubbed out API endpoint, /api/v1/hardware/{asset}/assigned/assets, allowing for retrieving assets assigned to a specific asset.

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In the process, I added a new query scope, applyOffsetAndLimit() on the base SnipeModel that allows the following snippet that appears at the end of a lot (most/all?) of our "index" api controller methods:

$total = $query->count();  
  
$offset = ($request->input('offset') > $total) ? $total : app('api_offset_value');  
$limit = app('api_limit_value');  
  
$assets = $query->skip($offset)->take($limit)->get();

to be simplified to:

$total = $query->count();  
  
$assets = $query->applyOffsetAndLimit($total)->get();

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Fixes #10052