feat(custom-rss): add custom xml tag injection in rss feed for ❬channel❭ and ❬item❭

app/Controllers/Admin/Episode.php

app/Controllers/Admin/Podcast.php

app/Database/Migrations/2020-05-30-101500_add_podcasts.php

app/Database/Migrations/2020-06-05-170000_add_episodes.php

app/Entities/Episode.php

app/Entities/Podcast.php

app/Helpers/rss_helper.php

app/Language/en/Episode.php

app/Language/en/Podcast.php

app/Language/fr/Episode.php

app/Language/fr/Podcast.php

app/Models/EpisodeModel.php

app/Models/PodcastModel.php

app/Views/admin/episode/create.php

app/Views/admin/episode/edit.php

app/Views/admin/podcast/create.php

app/Views/admin/podcast/edit.php