feat(reva): Pass the multi-tenancy flag to reva services

This allows to pass the multi-tenant enablement flag as a shared config
option to the reva service. This needs to be done for all reva services
since it ends up in a global variable in reva that is only initialized
once, by the service that is the first to parse its config.
See https://github.com/opencloud-eu/opencloud/issues/1563 for details.

services/frontend/pkg/revaconfig/config.go

@@ -93,6 +93,7 @@ func FrontendConfigFromStruct(cfg *config.Config, logger log.Logger) (map[string
 			"gatewaysvc":                cfg.Reva.Address, // Todo or address?
 			"skip_user_groups_in_token": cfg.SkipUserGroupsInToken,
 			"grpc_client_options":       cfg.Reva.GetGRPCClientConfig(),
+			"multi_tenant_enabled":      cfg.Commons.MultiTenantEnabled,
 		},
 		"http": map[string]interface{}{
 			"network": cfg.HTTP.Protocol,