Add video link for RailsConf 2024 (ruby-conferences#684)

Author: marcoroth

_data/conferences.yml

@@ -2530,6 +2530,7 @@
   cfp_open_date: 2024-01-24
   cfp_close_date: 2024-02-13
   cfp_link: https://sessionize.com/railsconf2024
+  video_link: https://www.youtube.com/playlist?list=PLbHJudTY1K0chrs_E_XFz2pOJ3d8jCayh
 
 - name: RubyKaigi 2024
   location: Naha, Okinawa, Japan