Support duplicating groups of fields

[sc0ttkclark]

Description

Allow duplicating groups of fields from REST API and from the admin UI.

Related GitHub issue(s)

#7322

Testing instructions

1. Edit a pod
2. Create a group with fields
3. Click "Duplicate" on that group row
4. See that a new group has been created below with a duplicate of all fields that original group contained

Screenshots / screencast

TBD

Changelog text for these changes

• Feature: Add new button to Duplicate Group from within the Pod editor Duplicate Groups within Pods/ #7322 (@sc0ttkclark)

PR checklist

• I have tested my own code to confirm it works as I intended.
• My code follows the WordPress Coding Standards.
• My code follows the WordPress Inline Documentation Standards.
• My code includes automated tests for PHP and/or JS (if applicable).

Remaining tasks

• Support updating the Pods object state with a new group
• Duplicate link should load the new group and it's fields into the admin area
• Show errors if one is encountered
• Update REST API endpoint to use /duplicate path and use a separate class to avoid POST collision with the group edit method