Add `maxIncomingAmount` on the incoming payment

[mkurapov]

Context

In order to allow the receiving ASE to specify the max incoming amount they would accept on an incoming payment, we decided to add in an optional maxIncomingAmount field on the incoming payment schema. This would get returned in the GET /incoming-payment call (the authorized/private version of that request), as well as the POST /incoming-payment call

Todos

• Add optional maxIncomingAmount field on the incoming payment schema.