Support a json string for field config

[JoryHogeveen]

Description

This PR allows a JSON string to be passed as a field configuration array for Pods Forms.

Related GitHub issue(s)

Fixes #6435

Testing instructions

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See '....'

Screenshots / screencast

Changelog text for these changes

• Support JSON as field configuration strings for the [pods_form] shortcode.

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).

[sc0ttkclark]

Looks good, let's be sure to set a changelog text entry in this PR description before merging

[JoryHogeveen]

@sc0ttkclark Done!

[sc0ttkclark]

This looks good but in practice, don't we have to contend with WP shortcodes handling of double quotes etc that JSON would be using?

The base branch was changed.

[JoryHogeveen]

Hi @sc0ttkclark Good point, will need to be tested