Updates config to use subcommands (#2146)

* First commit updating `config` to use subcommands (#2119)
    - Implemented `get` subcommand

* Implmented `config set` as a subcommand.

* Implemented `config set_into` as subcommand

* Fixed base `config` command
 - Instead of outputting help, it now outputs the list of all
 configuration parameters.

* Added `config clear` subcommand

* Added `config load` and `config remove` subcommands

* Added `config path` subcommand

* fixed clippy

crates/nu-cli/src/commands/config/load.rs

@@ -0,0 +1,59 @@
+use crate::commands::WholeStreamCommand;
+use crate::context::CommandRegistry;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{ReturnSuccess, Signature, SyntaxShape, UntaggedValue};
+use nu_source::Tagged;
+use std::path::PathBuf;
+
+pub struct SubCommand;
+
+#[derive(Deserialize)]
+pub struct LoadArgs {
+    load: Tagged<PathBuf>,
+}
+
+#[async_trait]
+impl WholeStreamCommand for SubCommand {
+    fn name(&self) -> &str {
+        "config load"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("config load").required(
+            "load",
+            SyntaxShape::Path,
+            "Path to load the config from",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Loads the config from the path given"
+    }
+
+    async fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        set(args, registry).await
+    }
+}
+
+pub async fn set(
+    args: CommandArgs,
+    registry: &CommandRegistry,
+) -> Result<OutputStream, ShellError> {
+    let name = args.call_info.name_tag.clone();
+    let name_span = args.call_info.name_tag.clone();
+    let (LoadArgs { load }, _) = args.process(&registry).await?;
+
+    let configuration = load.item().clone();
+
+    let result = crate::data::config::read(name_span, &Some(configuration))?;
+
+    Ok(futures::stream::iter(vec![ReturnSuccess::value(
+        UntaggedValue::Row(result.into()).into_value(name),
+    )])
+    .to_output_stream())
+}