[rails] Use 5 threads for puma (#10122)

This should score better for the fortunes test.

frameworks/Ruby/rails/rails-mysql.dockerfile

@@ -21,6 +21,7 @@ RUN bundle install --jobs=8
 COPY . /rails/
 
 ENV WEB_CONCURRENCY=auto
+ENV RAILS_MAX_THREADS=5
 ENV RAILS_ENV=production_mysql
 ENV PORT=8080
 ENV REDIS_URL=redis://localhost:6379/0

frameworks/Ruby/rails/rails.dockerfile

@@ -21,6 +21,7 @@ RUN bundle install --jobs=8
 COPY . /rails/
 
 ENV WEB_CONCURRENCY=auto
+ENV RAILS_MAX_THREADS=5
 ENV RAILS_ENV=production_postgresql
 ENV PORT=8080
 ENV REDIS_URL=redis://localhost:6379/0