Make pipeline metadata available to plugins (#13495)

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

crates/nu-protocol/src/pipeline/metadata.rs

@@ -1,7 +1,9 @@
 use std::path::PathBuf;
 
+use serde::{Deserialize, Serialize};
+
 /// Metadata that is valid for the whole [`PipelineData`](crate::PipelineData)
-#[derive(Debug, Default, Clone)]
+#[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
 pub struct PipelineMetadata {
     pub data_source: DataSource,
     pub content_type: Option<String>,
@@ -27,7 +29,7 @@ impl PipelineMetadata {
 ///
 /// This can either be a particular family of commands (useful so downstream commands can adjust
 /// the presentation e.g. `Ls`) or the opened file to protect against overwrite-attempts properly.
-#[derive(Debug, Default, Clone)]
+#[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
 pub enum DataSource {
     Ls,
     HtmlThemes,