allow sub-collections to be created from collection page

[blancoj]

Fixes #5492

When in a collection page, the user should be able to create a sub-collection.

The reason this was not working was because the code was checking for a nil value for child, but if there is no child the value to check for is false. The false value is set here in the code:

https://github.com/samvera/hyrax/blob/main/app/forms/hyrax/forms/dashboard/nest_collection_form.rb#L33

Guidance for testing, such as acceptance criteria or new user interface behaviors:

• Go to collection editing page.
• Clicking "Create new collection as subcollection"
• You should be able to create the new sub-collection.
• Go back to the collection page and you should see the newly created sub-collection displayed on this page.

@samvera/hyrax-code-reviewers

[elrayle]

Thanks for this fix.