Add subcommand to list local certificates

- Add `husk locals list` to list all certificates which would be used by
  husk, but are not introduced by another certificate. These
  certificates are added 'locally'.
- Refcator the code so that `local` -> `locals`.

src/commands/locals/add.rs

@@ -0,0 +1,12 @@
+use anyhow::Result;
+
+use crate::cli::cli_args::LocalsAddCommand;
+use crate::config::HuskConfigContainer;
+
+pub async fn dispatch(cmd: LocalsAddCommand, _config: &HuskConfigContainer) -> Result<()> {
+    println!("add");
+    println!("   {:?}", cmd.cert_file);
+    Ok(())
+}
+
+