Issue:
[FEATURE]: add `offset` field to mandates list

### Feature Description

The [mandates list](https://github.com/juspay/hyperswitch/blob/54c0b218d9f20c6388dde0f30ea525011cdad573/crates/router/src/routes/mandates.rs#L114) endpoint currently has no field to specify `offset`, which would skip certain number of entries from the start. This is necessary in order to provide pagination support.

### Possible Implementation

accept a field called `offset` which specifies the number of items to skip from the start.

This would be similar to the `payments_list` pagination. Refer [here](https://github.com/juspay/hyperswitch/blob/54c0b218d9f20c6388dde0f30ea525011cdad573/crates/router/src/routes/payments.rs#L868)

### Have you spent some time checking if this feature request 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?

None

Resolution:
<think>
PR Context:
- Title: feat(router): add offset in mandate list route
- Merged: 2024-03-19T07:56:00Z
- Files changed: 4 files
- Commits: 11 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Add offset to mandate list endpoint.
Closes #3748 

### Additional Changes

- [x] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!-
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** feat(router): add offset in mandate list route (#3923)
Files to modify:


**crates/api_models/src/mandates.rs**
  Modify existing code

**crates/router/src/db/mandate.rs**
  Modify existing code

**crates/router/src/routes/mandates.rs**
  Modify existing code

**crates/router/src/types/storage/mandate.rs**
  Modify existing code