Allow a type-bind to a custom field

[jlipka]

References

• (no issue given so far)
• Requires Allow a type-bind to a custom field DSpace#12631

Description

These changes (together with DSpace/DSpace#12631 ) allow you to create a type-bind inside a submission (workspace / workflow) to other fields than "dc.type".

Instructions for Reviewers

Take a look at DSpace/DSpace#12631 for an example configuration.

This pull request has been created as a draft. This version works well for us, but it may not be suitable for all cases or needs. Feel free to test and comment. As soon as someone gives an opinion i could remove the draft mode.

List of changes in this PR:

• The subscription to the related input fields is handled slightly differently to before. Instead of listening to the valueChanges of the related model, I changed the code to listen to the parent's array form control (if it exists!) to retrieve all the values of the child fields. Otherwise, handling any added or removed items would have been complicated and would have resulted in a lot more subscriptions.
• The valueChanges subscription is now delayed a little by using debounceTime to reduce the event processing

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