Chore: Bump to Shakapacker v7

[KevinMulhern]

1. Description of the Feature Request: A new major version of Shakapacker just dropped.

• Dependabot attempted to bump us but CI is failing
• Upgrade guide can be found here

2. Acceptance Criteria:

• [ ] CI passes with Shakapacker v7
• [ ] Review app builds with Shakapacker v7

[ahasunos]

I could help with this issue.

[ahasunos]

However, we have the latest version of Shakapacker here as 7.1.0 https://rubygems.org/gems/shakapacker/versions/7.1.0