feat(ddprobe): allow to manually specify gpu preference (#3521)

docs/configuration.md

@@ -848,6 +848,37 @@ editing the `conf` file in a text editor. Use the examples as reference.
     </tr>
 </table>
 
+### gpu_preference
+
+<table>
+    <tr>
+        <td>Description</td>
+        <td colspan="2">
+            Specify the GPU preference for the Sunshine process.
+            <br>
+            <br>
+            If set to negative number (-1 by default), Sunshine will try to detect the best GPU for the streamed display, but if it fails you will get a black screen.
+            <br>
+            Setting it to 0 will allow Windows to try and select the best GPU.
+            <br>
+            Setting it to 1 and above will prioritize the GPU that matches this number (the number has to be guessed, but it starts at 1 and increases).
+            @note{Applies to Windows only.}
+        </td>
+    </tr>
+    <tr>
+        <td>Default</td>
+        <td colspan="2">@code{}
+            -1
+            @endcode</td>
+    </tr>
+    <tr>
+        <td>Example</td>
+        <td colspan="2">@code{}
+            2
+            @endcode</td>
+    </tr>
+</table>
+
 ### output_name
 
 <table>