[Enhancement] Add option for a source to only use cookies when needed (#640)

* Updated model with new attribute

* Update app logic to use new cookie logic

* lots of tests

* Updated UI and renamed attribute

* Updated tests

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

@@ -87,10 +87,11 @@
     />
 
     <.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"
+      field={f[:cookie_behaviour]}
+      options={friendly_cookie_behaviours()}
+      type="select"
+      label="Cookie Behaviour"
+      help="Uses your YouTube cookies for this source (if configured). 'When Needed' tries to minimize cookie usage except for certain indexing and downloading tasks. See docs"
     />
 
     <section x-show="advancedMode">