SendGrid Suppression Group ID or Custom Unsubscribe URL

[efuller]

Description

When using the SendGrid email provider, they require either a suppression_group_id field or a custom_unsubscribe_url field to be sent in the request body

We should make this configurable on the SendGrid settings page and then add in the logic to allow the code to send the correct information to the API.

Use Case

When a user integrates SendGrid as their email provider, they should be able to configure a Custom Unsubscribe URL or a Suppression Group ID in the SendGrid settings page.

Acceptance Criteria

• Add fields to the SendGrid settings page when using the SendGrid adapter to allow an admin to configure the Custom Unsubscribe URL and the Suppression Group ID.
• Ensure the value of these fields make it to the API request that is sent to SendGrid.
• Create a unit test to confirm this functionality.