feat!: Make the url signing secret a mandatory config option

This is required for allowing the web office to download images to
insert into documents.

The secret is generated by `opencloud init` and the server refuses
to start now without a secret being set. (Breaking Change)

Also the setting is now moved to the shared options as all involved
services need the same secret to work properly.

Related: https://github.com/opencloud-eu/web/issues/704

services/ocdav/pkg/command/server.go

@@ -95,7 +95,7 @@ func Server(cfg *config.Config) *cli.Command {
 				ocdav.WithTraceProvider(traceProvider),
 				ocdav.RegisterTTL(registry.GetRegisterTTL()),
 				ocdav.RegisterInterval(registry.GetRegisterInterval()),
-				ocdav.URLSigningSharedSecret(cfg.URLSigningSharedSecret),
+				ocdav.URLSigningSharedSecret(cfg.Commons.URLSigningSecret),
 			}
 
 			s, err := ocdav.Service(opts...)