Make the Footer Block Customizable

[efuller]

Description

Currently, the footer block is hard-coded with unsubscribe / manage preferences links. How these links are constructed can/will change depending on the email provider being used. We would like to find a way to be able to easily change / adjust the output of the Footer Block.

Ideas

• Inner blocks?
• Filter the output?
• Add in a custom template file?

Use Case

When a user configures the plugin with a specific email provider, they should be able to customize the footer block in a way that will allow them to add in the necessary links that will allow users to be able to manage their email subscriptions.

Acceptance Criteria

• Ensure that the footer block's markup can be modified either by providers (which can substitute their own unsubscribe or manage preferences links) or by users who want a custom footer.