Create RunningKernel trait to allow for native and remote jupyter kernels (#20842)

Starts setting up a `RunningKernel` trait to make the remote kernel
implementation easy to get started with. No release notes until this is
all hooked up.

Release Notes:

- N/A

crates/repl/src/repl.rs

@@ -1,6 +1,6 @@
 pub mod components;
 mod jupyter_settings;
-mod kernels;
+pub mod kernels;
 pub mod notebook;
 mod outputs;
 mod repl_editor;