Add cursor shape configuration for each edit mode (#7745)

# Description

This PR allows the configuration of cursor shapes in nushell for each
edit mode. This is the change that is in the default_config.nu file.
```
  cursor_shape: {
    emacs: line # block, underscore, line (line is the default)
    vi_insert: block # block, underscore, line (block is the default)
    vi_normal: underscore # block, underscore, line  (underscore is the default)
  }
```

# User-Facing Changes

See above. If you'd prefer a different default, please speak up and let
us know.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-cli/src/prompt.rs

@@ -105,7 +105,7 @@ impl Prompt for NushellPrompt {
         if let Some(prompt_string) = &self.left_prompt_string {
             prompt_string.replace('\n', "\r\n").into()
         } else {
-            let default = DefaultPrompt::new();
+            let default = DefaultPrompt::default();
             default
                 .render_prompt_left()
                 .to_string()
@@ -118,7 +118,7 @@ impl Prompt for NushellPrompt {
         if let Some(prompt_string) = &self.right_prompt_string {
             prompt_string.replace('\n', "\r\n").into()
         } else {
-            let default = DefaultPrompt::new();
+            let default = DefaultPrompt::default();
             default
                 .render_prompt_right()
                 .to_string()