Issue: [BUG] mandate details are not persisted for Adyen connector

### Bug Description

This is specific to Adyen's connector integration.

In case mandate details were not present in the response of payment sync with Adyen, these details are sent through webhooks. However, these details are not being persisted in DB leading to MIT failures.

### Expected Behavior

Mandate details sent in the webhook's request should be persisted in payment_methods table for future MITs

### Actual Behavior

Mandate details sent in the webhook's request are not persisted in `payment_methods` table.

### Steps To Reproduce

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### Context For The Bug

_No response_

### Environment

Are you using hyperswitch hosted version? Yes/No
If yes, please provide the value of the `x-request-id` response header to help us debug your issue.

If not (or if building/running locally), please provide the following details:
1. Operating System or Linux distribution:
2. Rust version (output of `rustc --version`): ``
3. App version (output of `cargo r --features vergen -- --version`): ``


### Have you spent some time checking if this bug has been raised before?

- [X] I checked and didn't find a similar issue

### Have you read the Contributing Guidelines?

- [X] I have read the [Contributing Guidelines](https://github.com/juspay/hyperswitch/blob/main/docs/CONTRIBUTING.md)

### Are you willing to submit a PR?

Yes, I am willing to submit a PR!

Resolution: <think>
PR Context:
- Title: fix(connector): adyen - propagate connector mandate details in incoming webhooks
- Merged: 2024-12-02T18:30:38Z
- Files changed: 2 files
- Commits: 2 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
Described in the linked #6719 

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with corresponding changes.

Fo
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix(connector): adyen - propagate connector mandate details in incoming webhooks (#6720)
Files to modify:


**crates/router/src/connector/adyen.rs**
  Add:
    - function: private::get_mandate_details

**crates/router/src/connector/adyen/transformers.rs**
  Modify existing code