feat(namespace): handle request on vault namespace (#5)

* feat(namespace): handle request on vault namespace

action.yml

@@ -10,9 +10,12 @@ inputs:
   secrets:
     description: 'A semicolon-separated list of secrets to retrieve. These will automatically be converted to environmental variable keys. See README for more details'
     required: true
+  namespace:
+    description: 'The Vault namespace from which to query secrets. Vault Enterprise only, unset by default'
+    required: false
 runs:
   using: 'node12'
   main: 'dist/index.js'
 branding:
   icon: 'unlock'
-  color: 'gray-dark'
+  color: 'gray-dark'