Change aws-sdk-cloudwatch to development-only requirement

Gemfile

@@ -54,9 +54,9 @@ gem "uk_postcode"
 # For structured logging
 gem "lograge"
 
-# For AWS interactions
+# Use CloudWatch for metrics on form performance
 gem "aws-sdk-cloudwatch"
-gem "aws-sdk-codepipeline", "~> 1.91"
+# Use S3 for uploading form submissions as a file
 gem "aws-sdk-s3"
 
 # For sending submissions as CSV
@@ -86,6 +86,11 @@ group :development, :test do
   gem "brakeman", "~> 6.2"
 end
 
+group :development do
+  # For pipeline rake tasks
+  gem "aws-sdk-codepipeline", "~> 1.91"
+end
+
 group :test do
   # Use system testing [https://guides.rubyonrails.org/testing.html#system-testing]
   gem "capybara"