docs: add modules to usagestats

Author: JTorreG

source/usagestats.rst

@@ -20,6 +20,10 @@ available via the **GET**-only **/status** section of the
     * - Option
       - Description
 
+    * - **modules**
+      - Object;
+        list of currently loaded language modules.
+
     * - **connections**
       - Object;
         lists per-instance connection statistics.
@@ -37,6 +41,19 @@ Example:
 .. code-block:: json
 
    {
+       "modules": {
+           "python": [
+               {
+                   "version": "3.12.3",
+                   "lib": "/opt/unit/modules/python.unit.so"
+               },
+               {
+                   "version": "3.12.1",
+                   "lib": "/opt/unit/modules/python-3.12.1.unit.so"
+               }
+           ],
+       },
+
        "connections": {
            "accepted": 1067,
            "active": 13,
@@ -63,6 +80,29 @@ Example:
        }
    }
 
+Each item in the **modules** object lists one of the currently loaded language
+modules, the installed version (or versions) of the module, and the path to the
+module file:
+
+.. list-table::
+    :header-rows: 1
+
+    * - Option
+      - Description
+
+    * - **name**
+      - String;
+        language module name.
+
+    * - **version**
+      - String;
+        language module version. If multiple versions are loaded,
+        the list contains multiple items.
+
+    * - **lib**
+      - String;
+        path to the language module file.
+
 The **connections** object offers the following Unit instance metrics:
 
 .. list-table::