Remove dependency on Fieldmanager and manually create admin pages

[nikkifurls]

Description

Currently, Fieldmanager is used to generate the admin settings pages for WP Newsletter Builder.

We should remove the dependency on Fieldmanager and manually create the settings pages in the admin.

Use Case

When a developer installs WP Newsletter Builder they should not need to install any other plugins.

Comments

We could explore using Gutenberg for this edit page.

[kevinfodness]

For Alley folks, here is an example of where we did something similar (building an admin interface using Gutenberg on a settings page): https://l.alley.dev/2cdafe0d6c

[kevinfodness]

Would be good to use the useOption hook: https://github.com/alleyinteractive/alley-scripts/tree/main/packages/block-editor-tools/src/hooks/use-option

If we need to develop other hooks or helpers for working with settings pages using the Gutenberg editor, this would be a good opportunity to build those out in block-editor-tools (create additional issues in that repo to handle, then use them here).

[nikkifurls]

I expect a solution for this to be ready to review within the next couple of weeks! 👍

[nikkifurls]

The PR for this is updated, but is not ready for review.

I am working through an issue on the "Email Types" page, where the call to onChange(), which is defined in the useOption() hook, is not causing the component to refresh, which results in form values being unable to be updated. This functionality normally works properly if the value being updated is a scalar type. But in this case, the value is an array, and it isn't working properly. (@mboynes or @kevinfodness if you have any ideas on this issue, I'd love to hear them!)

In addition to resolving that issue, in order to get this across the finish line, we also need to:

• Extract the ImagePicker functionality to the MediaPicker component in block-editor-tools. See relevant Slack convo with @kevinfodness.
• Update CHANGELOG.md and plugin.php