Add Tickets domain for the voucher-based ticket shop (#8)

Reviewed-on: #8
Co-authored-by: Patrick Mueller <patrick@mueller-patrick.tech>
Co-committed-by: Patrick Mueller <patrick@mueller-patrick.tech>

.env.example

@@ -19,6 +19,10 @@ SALESFORCE_API_URL=
 SALESFORCE_CLIENT_ID=
 SALESFORCE_CLIENT_SECRET=
 
+TICKETS_DB=
+TICKETS_RATE_LIMIT_MAX=10
+TICKETS_RATE_LIMIT_WINDOW_MIN=10
+
 MEMBER_CREDENTIAL=123
 CHOIR_CREDENTIAL=123
 MANAGEMENT_CREDENTIAL=123