Add registration dates

Author: dgrizzanti

data/events/2025/philadelphia/main.yml

@@ -47,7 +47,7 @@ event_twitter: "DevOpsDaysPHL" # This will create a traditional "Follow" twitter
 nav_elements: # List of pages you want to show up in the navigation of your page.
  # - name: propose
  # - name: location
- # - name: registration
+  - name: registration
  # - name: program
  # - name: speakers
   - name: sponsor