[Enhancement] Use cookies on a per-source basis (#354)

* Added 'use_cookies' column to source

* Added cookies to the source form

* Updated every command to optionally include cookies

* LOTS of tests

* Made YT cookies off by default

lib/pinchflat_web/controllers/sources/source_html/source_form.html.heex

@@ -86,6 +86,13 @@
       help="Unchecking still indexes media but it won't be downloaded until you enable this option"
     />
 
+    <.input
+      field={f[:use_cookies]}
+      type="toggle"
+      label="Use Cookies for Downloading"
+      help="Uses your YouTube cookies for this source (if configured). Used for downloading private playlists and videos. See docs for important details"
+    />
+
     <.input
       field={f[:download_cutoff_date]}
       type="text"