feat: Document Editor Button Registration API

[josephfusco]

These changes include:

• [X] new API for registering buttons within the Document Editor
• [X] refactor plugin architecture to be "contributor first"
• [X] implement caching strategies in relevant GitHub workflows
• [x] pre-existing button e2e tests in main are passing

[jasonbahl]

This PR introduces the registerDocumentEditorToolbarButton access function.

This function allows registering a new editor toolbar button with the following parameters:

• name (string): The name of the button to register.
• config (Object): The configuration object for the button.
• priority (number, optional): The priority for the button, with lower numbers meaning higher priority. Default is 10.

Example usage:

const { registerDocumentEditorToolbarButton } = window.WPGraphQLIDE;

registerDocumentEditorToolbarButton( 'toggle-auth', toggleAuthButton, 1 );