SSH tunnel: use the maximum of the server timeout and the shutdown delay (#4477)

## Changes
If someone sets a very long shutdown delay (longer than the default 24h
server timeout), the job should not time out before the shutdown delay
can take effect

## Why
Some customers want to keep ssh workloads for longer that 24 hours and
we should respect that.

## Tests
Existing suite

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Author: ilia-db

experimental/ssh/cmd/connect.go

@@ -73,7 +73,7 @@ the SSH server and handling the connection proxy.
 			MaxClients:           maxClients,
 			HandoverTimeout:      handoverTimeout,
 			ReleasesDir:          releasesDir,
-			ServerTimeout:        serverTimeout,
+			ServerTimeout:        max(serverTimeout, shutdownDelay),
 			AutoStartCluster:     autoStartCluster,
 			ClientPublicKeyName:  clientPublicKeyName,
 			ClientPrivateKeyName: clientPrivateKeyName,