Make pipeline metadata available to plugins (#13495)

# Description
Fixes an issue with pipeline metadata not being passed to plugins.

crates/nu_plugin_nu_example/nu_plugin_nu_example.nu

@@ -7,7 +7,7 @@
 # language without adding any extra dependencies to our tests.
 
 const NUSHELL_VERSION = "0.96.2"
-const PLUGIN_VERSION = "0.1.0" # bump if you change commands!
+const PLUGIN_VERSION = "0.1.1" # bump if you change commands!
 
 def main [--stdio] {
   if ($stdio) {
@@ -133,7 +133,7 @@ def process_call [
 
   # Create a Value of type List that will be encoded and sent to Nushell
   let value = {
-    Value: {
+    Value: [{
       List: {
         vals: (0..9 | each { |x|
           {
@@ -157,7 +157,7 @@ def process_call [
         }),
         span: $span
       }
-    }
+    }, null]
   }
 
   write_response $id { PipelineData: $value }
@@ -265,4 +265,4 @@ def start_plugin [] {
     }) |
     each { from json | handle_input } |
     ignore
-}
+}