Move mechanize in Gemfile

We want this command to be available in the production environment so we
can start to get away from maving to check in new versions into Mavis.
The list of schools in Mavis should be independent of the released
version.

Jira-Issue: MAV-1257

Author: misaka

Gemfile

@@ -44,6 +44,7 @@ gem "govuk_design_system_formbuilder"
 gem "govuk_markdown"
 gem "jsonb_accessor"
 gem "jwt"
+gem "mechanize"
 gem "notifications-ruby-client"
 gem "okcomputer"
 gem "omniauth_openid_connect"
@@ -85,7 +86,6 @@ group :development do
   gem "aws-sdk-rds", "~> 1"
   gem "aws-sdk-s3", "~> 1"
   gem "hotwire-livereload"
-  gem "mechanize"
   gem "prettier_print", require: false
   gem "rladr"
   gem "rubocop-govuk", require: false