[QA] bump desktop client minimum version accepted by server

Some distros and some customers use very old, unsupported clients.
Obviously, this results in a bad user experience. There are still clients out there that don't support spaces! And OCIS happily serves them.

The client teams only maintain the latest release. Therefor, I suggest that the server blocks clients that don't support spaces or have known issues, and in the case of deprecated clients, the admins get notified.

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The server currently has a config.sample.php with minimum 2.3.3 (unchanged since 2018)
Users of client 2.3.3 suffer from a very old and unsupported client, but technically I'd expect that it would still work with sever 10.9.1

The situation is untested, no incompatibilities known.

@hodyroff recommends: The product owner for the client decides it.
its a classic where we weigh between functions, convinience and technical incapabilities