Allow new Valkyrie works to add existing members

[eliotjordan]

Descriptive summary

When creating a new Valkyrie work, allow users to attach existing works as children. This would happen in the form under the Relationships tab. Will need to add the update_work_members transaction step to the create_valkyrie_work step args.

Related work

https://github.com/samvera/hyrax/pull/5547

[elrayle]

I think this might be fixed. Need verification.

[rjkati]

I tested this on nurax-pg and was able to add an existing work as a child via the Relationships tab.