fix(video-clips): create unique temporary files for resources to be deleted after generation

- tempfile uniqueness ensures that each process lives in its independent context
- add
writable/temp folder to store video clips temporary resources
- add videoClipWorkers config to
Admin for specifying the number of ffmpeg processes to run in parallel
- update video clip preview
background to better suit the end result

modules/Admin/Config/Admin.php

@@ -15,4 +15,10 @@ class Admin extends BaseConfig
      * Defines a base route for all admin pages
      */
     public string $gateway = 'cp-admin';
+
+    /**
+     * Number of maximum ffmpeg processes to spawn in parallel when generating video clips. Processes are instance wide,
+     * meaning that they are shared across all podcasts and episodes.
+     */
+    public int $videoClipWorkers = 2;
 }