GST: Add ability to use other device providers

Signed-off-by: Vasiliy Doylov <nekocwd@mainlining.org>

README.md

@@ -14,6 +14,7 @@ Mostly made for PostmarketOS phones
   - `AUDIO_PROFILE` = `audio/x-ac3` - String - audio encoding
   - `CAM_CAPS` = auto max caps by default - String
   - `ONLY_FORMAT` = null - String, filter pixel formats to show only one (e.g `RGB`)
+  - `CAM_PROVIDER` = `pipewiredeviceprovider` - String, camera provider name (e.g `libcameraprovider`)
 
 ## Project TODO:
   - [ ] Fix cam/mode switching? (I can't reproduce errors)

src/gst.vala

@@ -82,7 +82,7 @@ public class EyeNeko.Gstreamer : Object {
         public static Camera[] get_all () {
             if (cameras == null) {
                 cameras = new Camera[0];
-                var pwprovider = Gst.DeviceProviderFactory.get_by_name ("pipewiredeviceprovider");
+                var pwprovider = Gst.DeviceProviderFactory.get_by_name (Env.get_variable_or ("CAM_PROVIDER", "pipewiredeviceprovider"));
                 pwprovider.start ();
                 foreach (var device in pwprovider.get_devices ()) {
                     if (device.has_classes ("Video/Source")) {