feat(auth): set up App Store modules

[biancadanforth]

Because:

• We want SubPlat to know about Apple IAP subscriptions for our RPs.

This commit:

• Sets up the needed Apple IAP modules in lib/payments/iap/apple-app-store including classes, their methods and types, largely modeled after the Google Play IAP modules.
• Adds App Store config (under config.subscriptions.appStore) including a sandbox flag and App Store credentials by app bundleId.
• Moves lib/payments/google-play to lib/payments/iap/google-play.
• Moves IAPConfig class to the new shared lib/payments/iap dir.
• Adds two new libraries to the auth server: app-store-server-api (App Store Server API client) and type-fest (for helpful TS types, such as RequireAtLeastOne used here).

Closes #10313, closes #12579

Checklist

Put an x in the boxes that apply

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

Screenshots (Optional)

Please attach the screenshots of the changes made in case of change in user interface.

Other information (Optional)

Here are the analogs I modeled the different modules on from the Google Play Store integration:

• AppleIAP ←→ PlayBilling
• SubscriptionPurchase ←→ SubscriptionPurchase
• PurchaseManager ←→ PurchaseManager/UserManager

[biancadanforth]

@bbangert I'm particularly interested in feedback on any parts that I can descope (e.g. if they are or can be covered by separate tickets) in order to land this sooner rather than later and unblock the other tickets.

[biancadanforth]

@bbangert : Here is the finished patch without tests and some questions for you. It'd be great if you can review this while I am working on fixing/adding tests. I'll ping you in Slack about this as well as we discussed.

Thank you in advance; I know this is a very large patch.

[biancadanforth]

Almost done with tests. I fixed (or attempted to in a couple of cases; see inline comments) the issues we discussed earlier today.

[biancadanforth]

I think we disabled squash and merge, but I can do an interactive rebase and roll these commits into one commit before merging.

I will file a follow-up ticket to set the App Store credentials/sandbox env vars in stage and prod and open a cloudops PR.

Edit: CloudOps ticket is https://mozilla-hub.atlassian.net/browse/FXA-4941 (#12594 ).

Updated the PR

[bbangert]

LGTM! Minor nit about the error, I'd imagine we'd figure it out quick if we did hit it since Apple purchase registration wouldn't work.