feat(refunds): Add refunds diesel model support in V2 API (#7503)

Co-authored-by: hyperswitch-bot[bot] <148525504+hyperswitch-bot[bot]@users.noreply.github.com>
Co-authored-by: Hrithikesh <61539176+hrithikesh026@users.noreply.github.com>
Files to modify:


**kv.rs**
  Modify existing code

**refund.rs**
  Add:
    - function: pub::update_with_id
    - function: pub::find_by_global_id
    - impl: impl Refund

**sample_data.rs**
  Modify existing code

**refund.rs**
  Add:
    - function: pub::update_with_id
    - function: pub::find_by_global_id
    - impl: impl Refund

**schema_v2.rs**
  Modify existing code

**kafka_store.rs**
  Add:
    - function: private::find_refund_by_id

**refund.rs**
  Add:
    - function: pub::update_with_id
    - function: pub::find_by_global_id
    - impl: impl Refund

**refund.rs**
  Add:
    - function: pub::update_with_id
    - function: pub::find_by_global_id
    - impl: impl Refund

**refund_event.rs**
  Add:
    - function: pub::from_storage
    - function: private::event_type
    - function: private::key
    - struct: pub::KafkaRefundEvent
    - impl: impl KafkaRefundEvent<'a>

**refund.rs**
  Add:
    - function: pub::update_with_id
    - function: pub::find_by_global_id
    - impl: impl Refund

**lib.rs**
  Add:
    - function: private::unique_constraints
    - function: private::table_name
    - impl: impl UniqueConstraints for diesel_models::Refund