Metadata / Bug: Person/Institution can be added several times

[Grizzly127]

We found out a bug, solving #165
Right now I can add a person, for example myself several times:

For example I add myself the first time as a rights owner and editor:

Then I can add myself again, because I forgot to give myself the contact person role without getting the information that the entry already exists and I can add the role as an editor again and I am shown there twice:

[HeyItsBATMAN]

What would be the intended behavior for this?

• Show an error when the entered agent is the same
• Change "Save" to "Update" when agent is the same (user might not notice the button changing though, and override existing fields)
• Something else?

[HeyItsBATMAN]

But I think this probably makes sense to delay until @vmalieske implements her metadata revision changes.

[HeyItsBATMAN]

The PR of @vmalieske regarding the metadata form has been merged, but there are still changes related to the agent form anyways. Let's discuss in the meeting how to proceed with this

[Grizzly127]

This issue is solved now, right @HeyItsBATMAN ?