add namespace param for fn and env (#2556)

This PR moves fission CLI as closer as possible to kubectl command behaviour.  We have improved namespace handling behaviour across CLI.

* add namespace param for fn and env
* use common fn for ns check
* update validation
* default namespace for httpTrigger, env and package, config and triggers
* use default ns
* add namespace filter to spec
* add forceNamespace flag
* set current namespace
* add default namespace in config
* add namespace specific destroy
* add all namespace in the list of resources
* add namespace as global tag
* use %s instead of %v
* add test cases for namespace
* use ns in get all functions

pkg/fission-cli/cmd/environment/command.go

@@ -81,7 +81,7 @@ func Commands() *cobra.Command {
 		RunE:  wrapper.Wrapper(List),
 	}
 	wrapper.SetFlags(listCmd, flag.FlagSet{
-		Optional: []flag.Flag{flag.NamespaceEnvironment},
+		Optional: []flag.Flag{flag.NamespaceEnvironment, flag.AllNamespaces},
 	})
 
 	listPodsCmd := &cobra.Command{