Update docs for some settings (#27293)

- update tooltips of `auto_install_extensions` , `active_pane_modifiers`
- update docs of `auto_install_extensions`, `active_pane_modifiers`,
`buffer_line_height`

Release Notes:

- N/A

---------

Co-authored-by: Kirill Bulatov <mail4score@gmail.com>

crates/extension_host/src/extension_settings.rs

@@ -12,6 +12,8 @@ pub struct ExtensionSettings {
     ///
     /// This is used to make functionality provided by extensions (e.g., language support)
     /// available out-of-the-box.
+    ///
+    /// Default: { "html": true }
     #[serde(default)]
     pub auto_install_extensions: HashMap<Arc<str>, bool>,
     #[serde(default)]