Remove hardcoded default email sender

And make it configurable via `action_mailer_default_from` config.

Closes #243

config/application-example.yml

@@ -145,6 +145,7 @@ auction_api_allowed_ips: '' # 192.0.2.0, 192.0.2.1
 action_mailer_default_protocol: # default: http
 action_mailer_default_host:
 action_mailer_default_port: # default: no port (80)
+action_mailer_default_from: # no-reply@example.com
 
 # Since the keys for staging are absent from the repo, we need to supply them separate for testing.
 test:
@@ -153,6 +154,7 @@ test:
   release_domains_to_auction: 'false'
   auction_api_allowed_ips: ''
   action_mailer_default_host: 'registry.test'
+  action_mailer_default_from: 'no-reply@registry.test'
 
 # Airbrake // Errbit:
 airbrake_host: "https://your-errbit-host.ee"

config/application.rb

@@ -90,6 +90,7 @@ module DomainNameRegistry
       domain:               ENV['smtp_domain'],
       openssl_verify_mode:  ENV['smtp_openssl_verify_mode']
     }
+    config.action_mailer.default_options = { from: ENV['action_mailer_default_from'] }
 
     config.action_view.default_form_builder = 'DefaultFormBuilder'
     config.secret_key_base = Figaro.env.secret_key_base

config/initializers/figaro.rb

@@ -12,4 +12,5 @@ Figaro.require_keys(%w[
   bank_statement_import_dir
   time_zone
   action_mailer_default_host
+  action_mailer_default_from
 ])