[FEATURE] Add support for sorting payments list by `modified_at`

[VenuMadhav2541]

Feature Description

In my use-case, I need to view payments sorted based on their most recent updates rather than their creation time.
Currently, the payments list API only supports sorting by created_at, which makes it difficult to identify payments that were recently modified due to status changes, refunds, captures, or other updates.

Adding support for sorting by modified_at would improve visibility into recently updated payments and make debugging/support workflows much easier.

Possible Implementation

• Extend the SortOn enum to include a Modified variant.
• Update the payment list query logic to support sorting by the modified_at field.
• Ensure both ascending and descending ordering is supported (SortBy::Asc and SortBy::Desc).
• Keep existing created_at sorting behavior unchanged as the default.

Have you spent some time checking if this feature request has been raised before?

• I checked and didn't find a similar issue

Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

Are you willing to submit a PR?

None

[krishpranav]

Hi, can i work on the issue?