Edited 2024-10-04: Parent ticket for subkey management improvements

I will add some subtasks for this. But since we also should have an interface to add an adsk.

This task should rename the "More details..." button in the certificate Details by a "Show subkeys" button for Public certificates and a "Manage subkeys" button for private certificates.
And in the subkey widget I would vote for adding a similar User Interface like we have for UserIDs with buttons instead of only the context menu to make the actions more discoverable.