Build stripe integration on backend side (#5246)

Adding stripe integration by making the server logic independent of the
input fields:
- query factories (remote server, foreign data wrapper, foreign table)
to loop on fields and values without hardcoding the names of the fields
- adding stripe input and type
- add the logic to handle static schema. Simply creating a big object to
store into the server

Additional work:
- rename username field to user. This is the input intended for postgres
user mapping and we now need a matching by name

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Co-authored-by: Thomas Trompette <thomast@twenty.com>

packages/twenty-server/src/engine/core-modules/feature-flag/feature-flag.entity.ts

@@ -21,6 +21,7 @@ export enum FeatureFlagKeys {
   IsEventObjectEnabled = 'IS_EVENT_OBJECT_ENABLED',
   IsAirtableIntegrationEnabled = 'IS_AIRTABLE_INTEGRATION_ENABLED',
   IsPostgreSQLIntegrationEnabled = 'IS_POSTGRESQL_INTEGRATION_ENABLED',
+  IsStripeIntegrationEnabled = 'IS_STRIPE_INTEGRATION_ENABLED',
   IsMultiSelectEnabled = 'IS_MULTI_SELECT_ENABLED',
 }