Custom API keys should be a table

[koppor]

The UI of our preferences for Custom API keys is not that good:

I would like to have a table. We have n < 10 fetchers with API keys, thus this is not a long list.

Catalog	Key	Use Custom Key
Biodiversity heritage	test	[x]
IEEE	other	[x]
Science direct	my	[x]

I also renamed "Custom" to "Use Custom Key", to make clear that the given key should be used.

[AbdAlRahmanGad]

Hi, I would love to work on this issue. Can you assign it to me?

[github-actions]

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