ENDPOINT -->: GET: All Invoices for Merchant Based on Status

This endpoint should:

render a JSON representation of all invoices for a given merchant that have a status matching the desired status query parameter
always return an array of data, even if one or zero resources are found
Only allow the status query parameter to be sent in, and only with the following values: shipped, returned or packaged
follow this pattern: GET /api/v1/merchants/:merchant_id/invoices?status=<status>

CCirbo / Little_Shop