Feature: add settings to enable connecting organizations through The Giving Block API

[glaubersilva]

Resolves GIVE-3068

Description

This PR adds content to the main tabs of The Giving Block integration that enables connecting new or existing organizations to the platform and also allows usersto delete from the DB all information related to a oraganization previously connected.

Affects

• The GiveWP > Settings > Payment Gateways > The Giving Block > Organization tab
• The GiveWP > Settings > Payment Gateways > The Giving Block > Options tab

Visuals

Testing Instructions

1. In your WP site, edit the wp-config.php file and set The Giving Block API to use the sandbox mode, like this: define('GIVE_TGB_CONNECT_MODE', 'sandbox');
2. Go to the settings page and onboarding, or connect an Organization (to make things easy in this step, just connect the GiveWP Sandbox organization using the following ID: 1189132016)
3. Now disconnect the GiveWP organization, delete all plugin data in the options tab, and make the onboarding of a new organization, and make sure the onboarding form works as expected.

IMPORTANT: is not possible make the onboarding with random data, it is necessary to use real organizations to make the onboarding form work, and we can find them on the http://candid.org/ website.

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[glaubersilva]

@jonwaldstein This is ready for a new review.

[jonwaldstein]

@glaubersilva thanks for the updates, looks good 👍