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

cmd/fission-cli/app/app.go

@@ -87,7 +87,7 @@ func App() *cobra.Command {
 	})
 
 	wrapper.SetFlags(rootCmd, flag.FlagSet{
-		Global: []flag.Flag{flag.GlobalServer, flag.GlobalVerbosity, flag.KubeContext},
+		Global: []flag.Flag{flag.GlobalServer, flag.GlobalVerbosity, flag.KubeContext, flag.Namespace},
 	})
 
 	groups := helptemplate.CommandGroups{}
@@ -101,7 +101,7 @@ func App() *cobra.Command {
 
 	flagExposer := helptemplate.ActsAsRootCommand(rootCmd, nil, groups...)
 	// show global options in usage
-	flagExposer.ExposeFlags(rootCmd, flagkey.Server, flagkey.Verbosity, flagkey.KubeContext)
+	flagExposer.ExposeFlags(rootCmd, flagkey.Server, flagkey.Verbosity, flagkey.KubeContext, flagkey.Namespace)
 
 	return rootCmd
 }