Upgrade to Rails 7.0

The config.file_watcher option still exists but it's no longer included
in the default environtment file. Since we don't use it, we're removing
it.

The config.assets.assets.debug option is no longer true by default [1],
so it isn't included anymore.

The config.active_support.deprecation option is now omitted on
production in favor of config.active_support.report_deprecations, which
is false by default. I think it's OK to keep it this way, since we check
deprecations in the development and test environments but never on
production environments.

As mentioned in the Rails upgrade guide, sprockets-rails is no longer a
rails dependency and we need to explicitly include it in our Gemfile.

The behavior of queries trying to find an invalid enum value has changed
[2], so we're updating the tests accordingly.

The `favicon_link_tag` method has removed the deprecated `shortcut`
link type [3], so we're updating the tests accordingly.

The method `raw_filter` in ActiveSupport callbacks has been renamed to
`filter` [4], so we're updating the code accordingly.

[1] https://github.com/rails/rails/commit/adec7e7ba87e3
[2] https://github.com/rails/rails/commit/b68f0954
[3] Pull request 43850 in https://github.com/rails/rails
[4] Pull request 41598 in https://github.com/rails/rails

db/migrate/20240322223950_remove_not_null_on_active_storage_blobs_checksum.active_storage.rb

@@ -0,0 +1,8 @@
+# This migration comes from active_storage (originally 20211119233751)
+class RemoveNotNullOnActiveStorageBlobsChecksum < ActiveRecord::Migration[6.0]
+  def change
+    return unless table_exists?(:active_storage_blobs)
+
+    change_column_null(:active_storage_blobs, :checksum, true)
+  end
+end