Issue: [FEAT] Add mandates for Payload

- Add MIT payments to Payload connector
- Add connector customer
- Fix amount conversion

Relevant docs:

- https://docs.payload.com/apis/payments/
- https://docs.payload.com/apis/payments/charging-a-customer/
- https://docs.payload.com/apis/automatic-payments/
- https://docs.payload.com/apis/customers/
- https://docs.payload.com/apis/object-reference/customers/
- https://docs.payload.com/apis/object-reference/transactions/
- https://docs.payload.com/apis/api-design/

Resolution: <think>
PR Context:
- Title: feat(connector): [payload] add recurring payments
- Merged: 2025-07-31T07:04:50Z
- Files changed: 23 files
- Commits: 29 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [x] CI/CD

## Description
<!-- Describe your changes in detail -->

This PR targets Payload connector and has multiple fixes and a new feature introduced:

- Add support for mandates (PMID and MandateID)
- Add filters
  - Enable connector customer
  - Enable mandates
  - Add currency filter
- Change A
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** feat(connector): [payload] add recurring payments (#8597)
Files to modify:


**crates/hyperswitch_connectors/src/connectors/payload.rs**
  Remove:
    - impl: impl ConnectorIntegration<Session, PaymentsSessionData, PaymentsResponseData> for Payload
  Add:
    - impl: impl ConnectorIntegration<Session, PaymentsSessionData, PaymentsResponseData> for Payload

**crates/hyperswitch_connectors/src/connectors/payload/requests.rs**
  Modify existing code

**crates/hyperswitch_connectors/src/connectors/payload/responses.rs**
  Modify existing code

**crates/hyperswitch_connectors/src/connectors/payload/transformers.rs**
  Remove:
    - struct: pub::PayloadAuthType
  Add:
    - function: private::try_from
    - function: private::try_from
    - struct: pub::PayloadAuth
    - struct: pub::PayloadAuthType
    - impl: impl TryFrom<(&ConnectorAuthType, enums::Currency)> for PayloadAuth
    - impl: impl TryFrom<&ConnectorAuthType> for PayloadAuthType

**crates/hyperswitch_connectors/src/default_implementations.rs**
  Modify existing code

**crates/hyperswitch_connectors/src/utils.rs**
  Add:
    - function: private::is_mandate_payment

**crates/hyperswitch_domain_models/src/router_request_types.rs**
  Modify existing code

**crates/router/tests/connectors/utils.rs**
  Modify existing code

**crates/test_utils/src/connector_auth.rs**
  Add:
    - function: private::from
    - impl: impl From<CurrencyAuthKey> for ConnectorAuthType