MM-21285: Remove environment overrides before config broadcast (#13527)

While sending the config broadcast message across a cluster, we would
include the environment overrides in the config.

We fix this by exposing a config config store method to remove the overrides,
and then calling that before saving the config across the cluster.

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/config.go

@@ -395,6 +395,7 @@ func (a *App) SaveConfig(newCfg *model.Config, sendConfigChangeClusterMessage bo
 	}
 
 	if a.Cluster != nil {
+		newCfg = a.Srv.configStore.RemoveEnvironmentOverrides(newCfg)
 		err := a.Cluster.ConfigChanged(oldCfg, newCfg, sendConfigChangeClusterMessage)
 		if err != nil {
 			return err