Use auth v2 in subscription activation flow

[lmac012]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1205648422731273/task/1210723642420067?focus=true

Description

Steps to test this PR

• Build with staging patch from https://app.asana.com/1/137249556945/project/1209991789468715/task/1210448620621729?focus=true
• Go to settings -> I have a subscription
• Click "Add via Email"
• Verify that the app made request to api/auth/v2/.well-known/jwks.json
• Proceed with resotoring the subscription until the success screen is shown
• Verify that there were no requests to api/auth/access-token
• Verify that there were no more requests to api/auth/v2/.well-known/jwks.json
• Verify that the app settings show subscription in active state, VPN can be enabled, etc.

No UI changes

[lmac012]

• Use auth v2 in subscription activation flow #6366 👈 (View in Graphite)
• develop

This stack of pull requests is managed by Graphite. Learn more about stacking.

[cmonfortep]

LGTM

Left some comments to ensure we have good signals and the proper try-catch, but other than that, lgtm and testing went well.