add retrieve api support for relay

[ShankarSinghC]

/relay is a api that will be used to just forward the request sent by merchant without performing any application logic on it. This is particular to support the refunds for the payments that was directly performed with the connector (example stripe) with out hyperswitch involved during the payment flow.

This PR introduces changes to add a retrieve API for relay refunds.

The retrieve API will:

1. Return the relay status from our database when a retrieve call is made.
2. If force_sync = true is passed and the relay status is not in a terminal state in our system, the API will call the connector to fetch the latest status.

Flow

1. Merchant performs payment directly with processor and stores the payment reference id associated with it.
2. Merchant tiggers the refund through hyperswitch using the processor reference id for the payment.
3. Merchant makes retrieve call for the relay status

[ShankarSinghC]

Reopening the issue to link it to the hotfix pr