Slightly improve completion in settings.json (for lsp.<language-server>.) (#42263)

Document "any-typed" (`serde_json::Value`) "lsp" keys to include them in
json-language-server completions.

The vscode-json-languageserver seems to skip generically typed keys when
offering completion.

For this schema

```
    "LspSettings": {
        "type": "object",
        "properties": {
            ...
            "initialization_options": true,
            ...
         }
     }
```

"initialization_options" is not offered in the completion.

The effect is easy to verify by triggering completion inside:

```
    "lsp": {
        "basedpyright": {
           COMPLETE HERE
```

<img width="797" height="215" alt="image"
src="https://github.com/user-attachments/assets/d1d1391c-d02c-4028-9888-8869f4d18b0f"
/>

By adding a documentation string the keys are offered even if they are
generically typed:

<img width="809" height="238" alt="image"
src="https://github.com/user-attachments/assets/9a072da9-961b-4e15-9aec-3d56933cbe67"
/>

---

Note: I did some cursory research of whether it's possible to make
vscode-json-languageserver change behavior without success. IMO, not
offering completions here is a bug (or at minimal should be
configurable)

---

Release Notes:

- N/A

---------

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

crates/settings/src/settings_content/project.rs

@@ -26,6 +26,7 @@ pub struct ProjectSettingsContent {
     /// The following settings can be overridden for specific language servers:
     /// - initialization_options
     ///
+    ///
     /// To override settings for a language, add an entry for that language server's
     /// name to the lsp value.
     /// Default: null
@@ -108,7 +109,19 @@ pub struct WorktreeSettingsContent {
 #[serde(rename_all = "snake_case")]
 pub struct LspSettings {
     pub binary: Option<BinarySettings>,
+    /// Options passed to the language server at startup.
+    ///
+    /// Ref: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize
+    ///
+    /// Consult the documentation for the specific language server to see what settings
+    /// are supported.
     pub initialization_options: Option<serde_json::Value>,
+    /// Language server settings.
+    ///
+    /// Ref: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_configuration
+    ///
+    /// Consult the documentation for the specific LSP to see what settings
+    /// are supported.
     pub settings: Option<serde_json::Value>,
     /// If the server supports sending tasks over LSP extensions,
     /// this setting can be used to enable or disable them in Zed.