Update Partner extract function in Campaign class

[weerd]

FEATURE OVERVIEW

User Story

As a developer, I would like to be able to ask the getPartners() method for an array of all the partners that are affiliated with a Campaign.

Currently, due to how the dosomething_helpers_extract_field_data() function works, it will only pass the first or only partner id. Need to update the dosomething_helpers_extract_field_data() to allow grabbing the entire array of partners ids if we want to, or alternatively add logic to the function to account for multiple partners and return an array of ids if there is more than one.

Why This Matters

If there is more than one partner associated with a Campaign, we currently can not extract that data properly for the API.