feat: Add onStarted and onStopped events (#2273)

* feat: Add `onStarted` and `onStopped` events

* Implement `onStart` for Android

* Update CameraSession.kt

* Update CameraSessionDelegate.swift

package/ios/Core/CameraSessionDelegate.swift

@@ -21,6 +21,14 @@ protocol CameraSessionDelegate: AnyObject {
    Called when the [CameraSession] successfully initializes
    */
   func onSessionInitialized()
+  /**
+   Called when the [CameraSession] starts streaming frames. (isActive=true)
+   */
+  func onCameraStarted()
+  /**
+   Called when the [CameraSession] stopped streaming frames. (isActive=false)
+   */
+  func onCameraStopped()
   /**
    Called for every frame (if video or frameProcessor is enabled)
    */