Rename $env.config.explore_config to $env.config.explore (for consistency with $env.config.ls, $env.config.table etc.) (#7317)

# Description

* `$env.config.explore_config` renamed to `$env.config.explore`. This
follows the principle that config subrecords relating to single commands
(as this relates to `explore`) should be exactly named after the command
(see `ls`, `rm`, `table` etc.)
* In `into_config()`, moved the match arm relating to
`$env.config.explore` out of the "legacy options" section (which is
slated for removal in a later version).

# User-Facing Changes

`explore` is not in any public releases yet, so this has no end-user
impact.

# 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-protocol/src/config.rs

@@ -87,7 +87,7 @@ pub struct Config {
     pub show_banner: bool,
     pub show_clickable_links_in_ls: bool,
     pub render_right_prompt_on_last_line: bool,
-    pub explore_config: HashMap<String, Value>,
+    pub explore: HashMap<String, Value>,
 }
 
 impl Default for Config {
@@ -126,7 +126,7 @@ impl Default for Config {
             show_banner: true,
             show_clickable_links_in_ls: true,
             render_right_prompt_on_last_line: false,
-            explore_config: HashMap::new(),
+            explore: HashMap::new(),
         }
     }
 }
@@ -526,6 +526,13 @@ impl Value {
                             eprintln!("$env.config.{} is not a record", key)
                         }
                     }
+                    "explore" => {
+                        if let Ok(map) = create_map(value, &config) {
+                            config.explore = map;
+                        } else {
+                            eprintln!("$env.config.{} is not a record", key)
+                        }
+                    }
                     // Misc. options
                     "color_config" => {
                         if let Ok(map) = create_map(value, &config) {
@@ -813,13 +820,6 @@ impl Value {
                             eprintln!("$env.config.filesize_format is not a string")
                         }
                     }
-                    "explore_config" => {
-                        if let Ok(map) = create_map(value, &config) {
-                            config.explore_config = map;
-                        } else {
-                            eprintln!("$env.config.explore_config is not a map")
-                        }
-                    }
                     // End legacy options
                     x => {
                         eprintln!("$env.config.{} is an unknown config setting", x)