Set SECRET_KEY_BASE_DUMMY=1 for random value for build with rails 7.1

See: https://www.github.com/rails/rails/pull/46760

Note, we don't yet have require_master_key set to true, so this should
work for now.  We'll need to see if that changes when/if we add rails
configuration options going forward.

```
irb(main):003:0> Rails.application.config.require_master_key
=> false
```

Dockerfile

@@ -2,7 +2,8 @@ FROM registry.access.redhat.com/ubi9/ubi
 
 ENV TERM=xterm \
     APPLIANCE=true \
-    RAILS_USE_MEMORY_STORE=true
+    RAILS_USE_MEMORY_STORE=true \
+    SECRET_KEY_BASE_DUMMY=1
 
 # Force the sticky bit on /tmp - https://bugzilla.redhat.com/show_bug.cgi?id=2138434
 RUN chmod +t /tmp