feat: add enterprise billing (#939)

## Description

Add support for enterprise billing plans.

Enterprise billing plans by default get access to everything early
adopters do:
- Unlimited teams
- Unlimited documents

They will also get additional features in the future.

## Notes

Pending webhook updates to support enterprise onboarding.
Rolled back env changes `NEXT_PUBLIC_PROJECT` since it doesn't seem to
work.

packages/lib/constants/billing.ts

@@ -6,6 +6,5 @@ export enum STRIPE_CUSTOMER_TYPE {
 export enum STRIPE_PLAN_TYPE {
   TEAM = 'team',
   COMMUNITY = 'community',
+  ENTERPRISE = 'enterprise',
 }
-
-export const TEAM_BILLING_DOMAIN = 'billing.team.documenso.com';