Upgrade to Rails 6.1

Note that `Capybara.app_host` now returns `nil` by default and that
breaks tests using `lvh.me` or our custom `app_host` method, so we're
setting `Capybara.app_host` to the value it had in earlier versions of
Rails. I also haven't found a way to remove the code to set the
integration session host in relationable tests which I mentioned in
commit ffc14e499.

Also note that we now filter more parameters, and that they match
regular expressions, so filtering `:passw` means we're filtering
`passwd`, `password`, ...

config/environments/production.rb

@@ -1,3 +1,5 @@
+require "active_support/core_ext/integer/time"
+
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 
@@ -35,7 +37,7 @@ Rails.application.configure do
   config.assets.compile = false
 
   # Enable serving of images, stylesheets, and JavaScripts from an asset server.
-  # config.action_controller.asset_host = "http://assets.example.com"
+  # config.asset_host = "http://assets.example.com"
 
   # Specifies the header that your server uses for sending files.
   # config.action_dispatch.x_sendfile_header = "X-Sendfile" # for Apache
@@ -50,8 +52,8 @@ Rails.application.configure do
   # Configure force_ssl in secrets.yml
   config.force_ssl = Rails.application.secrets.force_ssl
 
-  # Use the lowest log level to ensure availability of diagnostic information
-  # when problems arise.
+  # Include generic and useful information about system operation, but avoid logging too much
+  # information to avoid inadvertent exposure of personally identifiable information (PII).
   config.log_level = :warn
 
   # Prepend all log lines with the following tags.
@@ -84,6 +86,12 @@ Rails.application.configure do
   # Send deprecation notices to registered listeners.
   config.active_support.deprecation = :notify
 
+  # Log disallowed deprecations.
+  config.active_support.disallowed_deprecation = :log
+
+  # Tell Active Support which deprecation messages to disallow.
+  config.active_support.disallowed_deprecation_warnings = []
+
   # Use default logging formatter so that PID and timestamp are not suppressed.
   config.log_formatter = ::Logger::Formatter.new