CHORE: Refactor RecordChooser to use built-in Wagtail components

[ababic]

About these changes

We currently use wagtail-generic-chooser, which has since had parts of it re-implemented in Wagtail. This PR refactors our custom RecordChooser views and widget to use the built-in stuff, allowing us to ditch wagtail-generic-chooser as a dependency.

How to check these changes

Head to the image library and use try interacting with the 'record' field there.

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[LeanneEmans]

@jamesbiggs and @ahosgood - I wonder if this was discussed yesterday in the Dev Stand up. Any idea what the future of this PR is please?

[ahosgood]

@LeanneEmans - Got to be honest here... I have no context for this but I completely understand the intention. Not quite sure I'd know what to expect to see in the record field or how to know if it works. 🤔

[jamesbiggs]

@LeanneEmans This PR isn't massively necessary. ATM we're using a third-party package called wagtail-generic-chooser which is fine to use, but Wagtail has kind of "absorbed" the package and uses elements from it in Wagtail itself. I think the idea here was to move to use the built-in Wagtail choosers, as we're then not relying on a third-party package. I can see Andy's done a lot of work on this, but this work is not urgent nor necessary. I think it was more of just a nice-to-have, but quite a major one in terms of the changes it'd bring in. I'd like to leave it here in draft in case any of us want to pick it up in the future.