NH-66480: add back method_missing but with strict regex rule

lib/solarwinds_apm/config.rb

@@ -283,6 +283,27 @@ def self.[]=(key, value)
       end
     end
     # rubocop:enable Metrics/AbcSize, Metrics/PerceivedComplexity, Metrics/CyclomaticComplexity
+
+    def self.method_missing(sym, *args)
+      class_var_name = "@@#{sym}"
+
+      if sym.to_s =~ /\A(.{1,20})=\z/
+        self[$1] = args.first
+      else
+        # Try part of the @@config hash first
+        if @@config.key?(sym)
+          self[sym]
+
+        # Then try as a class variable
+        elsif self.class_variable_defined?(class_var_name.to_sym)
+          self.class_eval(class_var_name)
+
+        # Congrats - You've won a brand new nil...
+        else
+          nil
+        end
+      end
+    end
   end
 end