Allow plugins to report their own version and store it in the registry (#12883)

# Description

This allows plugins to report their version (and potentially other
metadata in the future). The version is shown in `plugin list` and in
`version`.

The metadata is stored in the registry file, and reflects whatever was
retrieved on `plugin add`, not necessarily the running binary. This can
help you to diagnose if there's some kind of mismatch with what you
expect. We could potentially use this functionality to show a warning or
error if a plugin being run does not have the same version as what was
in the cache file, suggesting `plugin add` be run again, but I haven't
done that at this point.

It is optional, and it requires the plugin author to make some code
changes if they want to provide it, since I can't automatically
determine the version of the calling crate or anything tricky like that
to do it.

Example:

```
> plugin list | select name version is_running pid
╭───┬────────────────┬─────────┬────────────┬─────╮
│ # │      name      │ version │ is_running │ pid │
├───┼────────────────┼─────────┼────────────┼─────┤
│ 0 │ example        │ 0.93.1  │ false      │     │
│ 1 │ gstat          │ 0.93.1  │ false      │     │
│ 2 │ inc            │ 0.93.1  │ false      │     │
│ 3 │ python_example │ 0.1.0   │ false      │     │
╰───┴────────────────┴─────────┴────────────┴─────╯
```

cc @maxim-uvarov (he asked for it)

# User-Facing Changes

- `plugin list` gets a `version` column
- `version` shows plugin versions when available
- plugin authors *should* add `fn metadata()` to their `impl Plugin`,
but don't have to

# Tests + Formatting

Tested the low level stuff and also the `plugin list` column.

# After Submitting
- [ ] update plugin guide docs
- [ ] update plugin protocol docs (`Metadata` call & response)
- [ ] update plugin template (`fn metadata()` should be easy)
- [ ] release notes

tests/plugins/registry_file.rs

@@ -18,6 +18,13 @@ fn example_plugin_path() -> PathBuf {
     .expect("nu_plugin_example not found")
 }
 
+fn valid_plugin_item_data() -> PluginRegistryItemData {
+    PluginRegistryItemData::Valid {
+        metadata: Default::default(),
+        commands: vec![],
+    }
+}
+
 #[test]
 fn plugin_add_then_restart_nu() {
     let result = nu_with_plugins!(
@@ -149,7 +156,7 @@ fn plugin_rm_then_restart_nu() {
             name: "example".into(),
             filename: example_plugin_path,
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents.upsert_plugin(PluginRegistryItem {
@@ -157,7 +164,7 @@ fn plugin_rm_then_restart_nu() {
             // this doesn't exist, but it should be ok
             filename: dirs.test().join("nu_plugin_foo"),
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents
@@ -225,7 +232,7 @@ fn plugin_rm_from_custom_path() {
             name: "example".into(),
             filename: example_plugin_path,
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents.upsert_plugin(PluginRegistryItem {
@@ -233,7 +240,7 @@ fn plugin_rm_from_custom_path() {
             // this doesn't exist, but it should be ok
             filename: dirs.test().join("nu_plugin_foo"),
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents
@@ -273,7 +280,7 @@ fn plugin_rm_using_filename() {
             name: "example".into(),
             filename: example_plugin_path.clone(),
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents.upsert_plugin(PluginRegistryItem {
@@ -281,7 +288,7 @@ fn plugin_rm_using_filename() {
             // this doesn't exist, but it should be ok
             filename: dirs.test().join("nu_plugin_foo"),
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents
@@ -331,7 +338,7 @@ fn warning_on_invalid_plugin_item() {
             name: "example".into(),
             filename: example_plugin_path,
             shell: None,
-            data: PluginRegistryItemData::Valid { commands: vec![] },
+            data: valid_plugin_item_data(),
         });
 
         contents.upsert_plugin(PluginRegistryItem {