Recently we started giving admins a notice in the advice panel when their translations have become outdated due to changes in core. However, we didn't include any additional information.
This PR adds more information about the outdated translation inside the site text edit page, together with an option to dismiss the warning.
This is the first of a number of PRs aimed at helping admins manage their translation overrides. It simply adds a list of available interpolation keys below the input field when editing an override.
It also includes custom interpolation key.
"I18n.t(key, locale: locale)" fails to find the correct translation in some cases. We should always wrap it with the "I18n.with_locale(locale)" method.
Also, reverting an override wasn't always possible because the serializer always used "I18n.locale" as the locale.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
