Add named log tag for environment

This allows the various deployment environments to be distinguished in
the logs, since the `ENVIRONMENT` variable is consistent across both
development and production.

`config.log_tags` is a Ruby built-in which can be overridden as part of
Semantic Logger (see
https://rocketjob.github.io/semantic_logger/rails.html#named-tags) to
add additional parameters to all requests.

ENVIRONMENT_NAME is now also set to `local` in `.env.development`, so
developers working locally will have the variable set by default.

.env.development

@@ -8,3 +8,4 @@ DFE_SIGN_IN_API_CLIENT_ID=teacherpayments
 DFE_SIGN_IN_API_ENDPOINT=https://pp-api.signin.education.gov.uk
 
 ADMIN_ALLOWED_IPS=::1,127.0.0.1
+ENVIRONMENT_NAME=local

Dockerfile

@@ -103,6 +103,7 @@ RUN if [ ${RAILS_ENV} = "production" ]; then \
   DFE_SIGN_IN_API_SECRET= \
   DFE_SIGN_IN_API_ENDPOINT= \
   ADMIN_ALLOWED_IPS= \
+  ENVIRONMENT_NAME= \
   bundle exec rake assets:precompile; \
   fi
 

config/application.rb

@@ -50,5 +50,11 @@ class Application < Rails::Application
     config.action_view.form_with_generates_remote_forms = false
 
     config.guidance_url = "https://www.gov.uk/government/publications/additional-payments-for-teaching-eligibility-and-payment-details"
+
+    # Additional information which is passed in the logs for each request
+    # See https://rocketjob.github.io/semantic_logger/rails.html#named-tags
+    config.log_tags = {
+      environment: ENV.fetch("ENVIRONMENT_NAME", "unspecified"),
+    }
   end
 end