Create new related work items on new work item page

What does this MR do and why?

We can create new related work items in a modal via the 'actions menu' when viewing a work item.

The 'new work item' modal has a button/link that takes you to the full-page version of the 'new work item' form. This change makes sure the 'relates to' setting is persisted when navigating from the modal view, to the full page view.

References

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MR acceptance checklist

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Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Screen_Recording_2024-11-26_at_13.39.54

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Visit an Epic and use the action menu to open the 'new related epic' modal.
2. Click the 'open in full page' button beside the modal title.
3. Check that the 'relates to' checkbox is checked, and that creating the new epic also creates the correct relationship.
4. This should also work with Issues if you have Work Item based issues enabled (via the work_items_view_preference feature flag)

Related to #498697 (closed)