Add registration and cfp info for Blastoff Rails (ruby-conferences#1186)

Author: travisdock

_data/conferences.yml

@@ -3272,6 +3272,9 @@
   url: https://blastoffrails.com
   twitter: blastoffrails
   announced_on: 2025-07-09
+  cfp_open_date: 2025-09-15
+  cfp_close_date: 2026-01-10
+  cfp_link: https://www.papercall.io/blastoff
 
 - name: Baltic Ruby 2026
   location: Hamburg, Germany