Feature: add Constant Contact add-on to the form migration process

[JoshuaHungDinh]

Resolves: GIVE-176

Description

This PR includes a form migration step for the new Constant Contact block migrating from a v2 form to a v3 form. I also removed the commented section of supported addons for Constant Contact so that it will display on our list when upgrading.

Cases when the block should be added.

• While Constant Contact is globally enabled on all forms, if the form is not explicitly disabled from the per form setting migrating should add the block.
• While Constant Contact is not globally enabled if it is explicitly enabled on the per form setting than migrating should add the block.

Testing Instructions

• Use New Constant Contact Block
• Create a v2 form -> update the settings -> migrate the form to verify the new settings and block are added if they match one of the above cases. If not verify the block in not added to the new form.
• Verify Constant Contact icon is displayed as a supported addon.

Pre-review ChecklistT

• [x] Relevant @unreleased tags included in DocBlocks
• [x] Reviewed by the designer (if follows a design)
• [x] Self Review of code and UX completed