Allow Harvesting to use arbitrary sets

[scolapasta]

Currently the UI only alllows for sets that the server returns, This ticket is to verify and/add that you can definie an arbitrary set via the API (and eventually the UI, but that might wait for the SPA to support harvesting, unless it's quick in the current UI) to support sets defined for DataCite OAI.

[scolapasta]

So checking the API, we can add / edit a haresting client and should be able to set any set. We'll need to test it, once we have #10936 working to make sure.

Once thing I'm not sure if is how large these set names will be, right now the set field is set to:
harvestingset | character varying(255)

So if it needs to be longer, the one thing we can (proactively) consider is to change this to be type text.

[scolapasta]

Here is the guides link to the API:
https://guides.dataverse.org/en/latest/api/native-api.html#create-a-harvesting-client

[landreev]

I think we should just remove the length restriction on the set field proactively. Since the whole point here is that DataCite's implementation accepts "sets" that are in fact arbitrary search queries - so it's reasonable to expect that there will be a use case for a very long one; like a very long list of specific DOIs, for example.

[landreev]

Closing since the task described is part of the overall #10909 that's in progress.
(The issue of the set having a character limit has been noted as an item in the above).