Allow plugins to receive configuration from the nushell configuration (#10955)

# Description

When nushell calls a plugin it now sends a configuration `Value` from
the nushell config under `$env.config.plugins.PLUGIN_SHORT_NAME`. This
allows plugin authors to read configuration provided by plugin users.

The `PLUGIN_SHORT_NAME` must match the registered filename after
`nu_plugin_`. If you register `target/debug/nu_plugin_config` the
`PLUGIN_NAME` will be `config` and the nushell config will loook like:

        $env.config = {
          # ...
          plugins: {
            config: [
              some
              values
            ]
          }
        }

Configuration may also use a closure which allows passing values from
`$env` to a plugin:

        $env.config = {
          # ...
          plugins: {
            config: {||
              $env.some_value
            }
          }
        }

This is a breaking change for the plugin API as the `Plugin::run()`
function now accepts a new configuration argument which is an
`&Option<Value>`. If no configuration was supplied the value is `None`.

Plugins compiled after this change should work with older nushell, and
will behave as if the configuration was not set.

Initially discussed in #10867

# User-Facing Changes

* Plugins can read configuration data stored in `$env.config.plugins`
* The plugin `CallInfo` now includes a `config` entry, existing plugins
will require updates

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

- [ ] Update [Creating a plugin (in
Rust)](https://www.nushell.sh/contributor-book/plugins.html#creating-a-plugin-in-rust)
[source](https://github.com/nushell/nushell.github.io/blob/main/contributor-book/plugins.md)
- [ ] Add "Configuration" section to [Plugins
documentation](https://www.nushell.sh/contributor-book/plugins.html)

tests/plugins/config.rs

@@ -0,0 +1,56 @@
+use nu_test_support::nu_with_plugins;
+
+#[test]
+fn closure() {
+    let actual = nu_with_plugins!(
+        cwd: "tests",
+        plugin: ("nu_plugin_example"),
+        r#"
+            $env.env_value = "value from env"
+
+            $env.config = {
+                plugins: {
+                    example: {||
+                        $env.env_value
+                    }
+                }
+            }
+            nu-example-config
+        "#
+    );
+
+    assert!(actual.out.contains("value from env"));
+}
+
+#[test]
+fn none() {
+    let actual = nu_with_plugins!(
+        cwd: "tests",
+        plugin: ("nu_plugin_example"),
+        "nu-example-config"
+    );
+
+    assert!(actual.err.contains("No config sent"));
+}
+
+#[test]
+fn record() {
+    let actual = nu_with_plugins!(
+        cwd: "tests",
+        plugin: ("nu_plugin_example"),
+        r#"
+            $env.config = {
+                plugins: {
+                    example: {
+                        key1: "value"
+                        key2: "other"
+                    }
+                }
+            }
+            nu-example-config
+        "#
+    );
+
+    assert!(actual.out.contains("value"));
+    assert!(actual.out.contains("other"));
+}