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/flag/key/key.go

@@ -38,6 +38,10 @@ const (
 	NamespacePackage     = "pkgNamespace"
 	NamespaceTrigger     = "triggerNamespace"
 	NamespaceCanary      = "canaryNamespace"
+	Namespace            = "namespace"
+	ForceNamespace       = "force-namespace"
+	AllNamespaces        = "all-namespaces"
+	ForceDelete          = "force"
 
 	RuntimeMincpu    = "mincpu"
 	RuntimeMaxcpu    = "maxcpu"