feat(router): Add support for network token migration

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [x] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Add support for network token migration.

### Additional Changes

- [x] 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.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
-->


## How did you test it?
<!--
Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->
test migration api.
req - 
```
curl --location 'http://localhost:8080/payment_methods/migrate' \
--header 'Content-Type: application/json' \
--header 'Accept: application/json' \
--header 'api-key: api-key' \
--data '{
    "merchant_id": "merchant_id",
    "card": {
        "card_number": "card_number",
        "card_exp_month": "12",
        "card_exp_year": "21",
        "card_holder_name": "joseph Doe"
    },
    "customer_id": "customer_id",
    "network_transaction_id": "nt-transaction-id",
    "payment_method": "card",
    "network_token": {
        "network_token_data": {
            "network_token_number": "network_token_number",
            "network_token_exp_month": "12",
            "network_token_exp_year": "21"
        },
        "network_token_requestor_ref_id": "test-ref-id"
    }
}'
```
expected response - 
```
{
    "payment_method_response": {
        "merchant_id": "merchant_1731400520",
        "customer_id": "cust-1731400905",
        "payment_method_id": "pm_LSk7YuLskFS8aBdWNvzk",
        "payment_method": "card",
        "payment_method_type": null,
        "card": {
            "scheme": null,
            "issuer_country": null,
            "last4_digits": "0000",
            "expiry_month": "12",
            "expiry_year": "21",
            "card_token": null,
            "card_holder_name": "joseph Doe",
            "card_fingerprint": null,
            "nick_name": null,
            "card_network": null,
            "card_isin": "420000",
            "card_issuer": null,
            "card_type": null,
            "saved_to_locker": true
        },
        "recurring_enabled": false,
        "installment_payment_enabled": false,
        "payment_experience": [
            "redirect_to_url"
        ],
        "metadata": null,
        "created": "2024-11-12T09:00:50.948Z",
        "last_used_at": "2024-11-12T09:00:50.949Z",
        "client_secret": "pm_LSk7YuLskFS8aBdWNvzk_secret_6B5AfKanyCDhy5hjeUce"
    },
    "card_migrated": true,
    "network_token_migrated": true,
    "connector_mandate_details_migrated": null,
    "network_transaction_id_migrated": true
}
```
<img width="1148" alt="Screenshot 2024-11-12 at 2 31 12 PM" src="https://github.com/user-attachments/assets/e3661f77-075e-4768-bac1-c2b23e0c12ce">


## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible

<think>
PR Context:
- Title: fix(router): validate each field for migration request body
- Merged: 2024-12-06T11:44:36Z
- Files changed: 1 files
- Commits: 15 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
<!-- Describe your changes in detail -->
#6300 has inconsistent response due to no validations for each field in migration api request body.

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies applic
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix(router): validate each field for migration request body (#6525)
Co-authored-by: hyperswitch-bot[
Files to modify:


**crates/router/src/core/payment_methods/cards.rs**
  Modify existing code
{"issue_number": 6300, "pr_number": 6525, "commits_count": 1, "files_changed": 1, "response_length": 987, "file_count": 3, "needs_breakdown": false}