Edit-bitstream-page component is difficult to theme #4101
Description
The edit-bitstream-page component is very difficult to theme at the moment.
When an additional field has to be added to add additional metadata to the bitstream, nearly all methods have to be overridden.
In addition, due to the way the methods are structured there are some difficult-to-spot nested observable subscriptions.
For example:
The ngOnInit method creates multiple observables, and subscribes to them immediately to 'set the IIIF status'.
The setIiifStatus method then creates some more observables (some of which containing data that has been retrieved previously) and again subscribes to them in the same method to continue with 'setting the form'.
This chain of method calls continues with updateForm and updateFormatLayout.
The onSubmit method is another long method making use of multiple observables and an immediate subscription.