[RIL-714] Add BOOT_ONLY_FROM_VOLUME parameter

Adds parameter that disables all boot options except boot from volume
diff --git a/horizon/files/horizon_settings/_local_settings.py b/horizon/files/horizon_settings/_local_settings.py
index ca999c3..14b317c 100644
--- a/horizon/files/horizon_settings/_local_settings.py
+++ b/horizon/files/horizon_settings/_local_settings.py
@@ -208,3 +208,4 @@
 SITE_DETAILS = "{{ app.site_details }}"
 {%- endif %}
 SESSION_COOKIE_HTTPONLY = {{ app.get('session_cookie_httponly', True) }}
+BOOT_ONLY_FROM_VOLUME = {{ app.get('boot_only_from_volume', True) }}