Payments/subscriptions support (#943)

* [wip] Payments/subscriptions support

* finish

* working payment flow

* finish subscriptions, lint, clippy, etc

* docker compose

src/models/v3/mod.rs

@@ -1,4 +1,5 @@
 pub mod analytics;
+pub mod billing;
 pub mod collections;
 pub mod ids;
 pub mod images;