Move to open source happo account

[BCerki]

Description

As a toolkit contributor
I want to use the happo open source plan
So that I can have continued access to happo

Tasks (How)

• Determine if Button already has a happo account
• If yes, update the repo secrets to use the Button account
• If not, talk to happo about setting up an open-source account: https://happo.io/pricing#:~:text=Can%20I%20use,get%20things%20started.