refactor(relay): add trait based implementation for relay (#7264)

Co-authored-by: hyperswitch-bot[bot] <148525504+hyperswitch-bot[bot]@users.noreply.github.com>
Files to modify:


**relay.rs**
  Remove:
    - struct: pub::RelayRefundRequest
  Add:
    - struct: pub::RelayRefundRequestData

**merchant_connector_account.rs**
  Add:
    - function: pub::get_connector_name_as_string
    - function: pub::get_connector_name_as_string

**relay.rs**
  Remove:
    - struct: pub::RelayRefundRequest
  Add:
    - struct: pub::RelayRefundRequestData

**openapi.rs**
  Modify existing code

**relay.rs**
  Remove:
    - struct: pub::RelayRefundRequest
  Add:
    - struct: pub::RelayRefundRequestData

**relay.rs**
  Remove:
    - struct: pub::RelayRefundRequest
  Add:
    - struct: pub::RelayRefundRequestData