Adding a textbox / textarea somewhere on the edit screen for a change log

I’ve made a plugin which includes a text box on the old WordPress editor to allow the user to leave a revision note when they edit a post. This involved appending some HTML underneath one of the built-in metaboxes, and as such it no longer works with Gutenberg.

I’ve tried to search for some advice on how best to add such a textbox or textarea to the Gutenberg editor, but I can’t find anything so far. I don’t really mind where this textbox goes – it could go on the sidebar, at the bottom or on a box that appears before publishing – but I want to use whatever approach is best intended by the Gutenberg developers.

Does anyone have any advice on which hooks to look at? Is this approach even supported by Gutenberg?