Add shallow clone option

## Overview

Add a shallow clone option that can leverage the [`shallow_days` functionality in the framework](https://github.com/ComplianceAsCode/auditree-framework/blob/main/compliance/locker.py#L568-L574).

## Requirements

TBD

## Approach

TBD

## Security and Privacy

N/A

## Test Plan

TBD

Start by reading the framework's compliance/locker.py lines 568-574 and locate where auditree-plant configures cloning. The issue provides no requirements or test plan; completion should include a shallow clone option that leverages the framework's shallow_days functionality and appropriate validation.

Written by the indexing model from the issue text.