Avoid [ActiveSupport::OrderedOptions#dig]

The implementation has been updated upstream[^1] to expect symbolized
keys. MRSK relies heavily on the fact that nested keys are strings, so
we're removing existing uses of `#dig`.

[^1]: 5c15b586aa

lib/mrsk/configuration.rb

@@ -165,6 +165,9 @@ class Mrsk::Configuration
     }.compact
   end
 
+  def traefik
+    raw_config.traefik || {}
+  end
 
   private
     # Will raise ArgumentError if any required config keys are missing