[ruby/rack] Use 2 threads for Iodine (#10508)

Instead of having more workers than processes, run with more threads.

Author: p8

frameworks/Ruby/rack/hello_world.rb

@@ -45,6 +45,8 @@ class HelloWorld
   def initialize
     if defined?(Puma) || defined?(Itsi)
       max_connections = ENV.fetch('MAX_THREADS')
+    elsif defined?(Iodine)
+      max_connections = ENV.fetch('THREADS')
     else
       max_connections = 512
     end

frameworks/Ruby/rack/rack-iodine.dockerfile

@@ -17,6 +17,8 @@ RUN bundle install --jobs=8
 
 COPY . .
 
+ENV THREADS=2
+
 EXPOSE 8080
 
-CMD bundle exec iodine -p 8080 -w $(($(nproc)*5/4))
+CMD bundle exec iodine -p 8080 -w $(nproc)