Add update_contact_list endpoint to add user to a list

[robypez]

Missing endpoint that i need for my project

[qlty-cloud-legacy[bot]]

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[Willardgmoore]

I'm new to active campaign. @robypez Should I be looking into this gem or the active-campaign-rails gem, or just build it directly into the system? I'm not sure if this gem is working based on the status and dates I'm seeing on requests, commits, etc

[mhenrixon]

I'd accept the PR with test coverage and a working implementation: https://developers.activecampaign.com/reference#update-list-status-for-contact

Right now, it seems the implementation is broken.