Fix nushell local env detection by using direnv export (#13902)

I don't intend fully on getting this merged, this is just an experiment
on using `direnv` directly without relying on shell-specific behaviours.
It works though, so this finally closes #8633
Release Notes:

- Fixed nushell not picking up `direnv` environments by directly
interfacing with it using `direnv export`

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/project/src/project_settings.rs

@@ -20,6 +20,23 @@ pub struct ProjectSettings {
     /// Configuration for Git-related features
     #[serde(default)]
     pub git: GitSettings,
+
+    /// Configuration for how direnv configuration should be loaded
+    #[serde(default)]
+    pub load_direnv: DirenvSettings,
+}
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum DirenvSettings {
+    /// Load direnv configuration through a shell hook
+    #[default]
+    ShellHook,
+    /// Load direnv configuration directly using `direnv export json`
+    ///
+    /// Warning: This option is experimental and might cause some inconsistent behaviour compared to using the shell hook.
+    /// If it does, please report it to GitHub
+    Direct,
 }
 
 #[derive(Copy, Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]