chore: API improvements (#3637)

- Unique validations for Inbox members and Team member objects
- Move notification processing to Async

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_12_19_031453) do
+ActiveRecord::Schema.define(version: 2021_12_21_125545) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
@@ -429,6 +429,7 @@ ActiveRecord::Schema.define(version: 2021_12_19_031453) do
     t.integer "inbox_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["inbox_id", "user_id"], name: "index_inbox_members_on_inbox_id_and_user_id", unique: true
     t.index ["inbox_id"], name: "index_inbox_members_on_inbox_id"
   end