Issue:
feat(core): add backwards compatibility for multiple mca

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] New feature

## Description
<!-- Describe your changes in detail -->
This will use default values if not passed in the request if feature `backwards_compatibality` is enabled. If not then the additional fields will be mandatory.


## 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 its an obvious bug or documentation fix
that will have little conversation).
-->
To support backwards compatibality

## 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)?
-->
- Run the application with `backwards_compatible` feature
- Create a merchant account without business details -> autopopulated
- Create a merchant connector account without business details -> autopopulated
- Create a payment without business details -> taken from merchant account.

## 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 submitted code


Resolution:
<think>
PR Context:
- Title: Changelog for release v0.5.6
- Merged: 2023-04-17T06:54:49Z
- Files changed: 1 files
- Commits: 10 commits

Implementation approach:
# 0.5.6 2023-04-14

## Build System / Dependencies

* **deps:**  bump `fred` from `5.2.0` to `6.0.0` (#869) (01bc162d)

## Continuous Integration

* **manual_release:**  add `multiple_mca` feature in ci (#872) (aebb4dca)

## New Features

* **core:**  add backwards compatibility for multiple mca (#866) (cf902f19)
* **router:**
  *  added dispute retrieve and dispute list apis (#842) (acab7671)
  *  separate straight through algorithm in separate column in payment attempt (#863) (0
</think>

To implement this, you'll need to modify:


(No detailed commit information available)