Support recurring monthly amount

[Radu-Cristian Popa]

Context

When connecting their wallet, users can opt-in for a recurring monthly amount.

Todos

• When receiving the CONNECT_WALLET message (from popup to background) verify if the recurring property is true:
  • if true: generate a monthly repeating interval having the current date as a start date (ISO 8601);
  • if false do not generate the interval - meaning that the user opted in for a one time amount;
• Make sure to specify the interval when requesting the outgoing payment grant (https://openpayments.guide/apis/auth-server/operations/post-request/#request-body);

[tselit]

Aiming to have this ready for review by the end of this week, 19 Apr.

[tselit]

On track to go into review tomorrow, Fri, 19 Apr.