Localizing the date in the enforcement banner

What does this MR do and why?

This is a follow-up from !122964 (comment 1422781252):

One suggestion, though, it would be best if the finish date of the offer was localized. The date format YYYY-MM-DD is certainly our standard, but it may be more easily understood if it was localized.

From @dstull:

you can use this if you desire offer_date: l(Date.new(2023, 8, 13), format: Date::DATE_FORMATS[:medium]) and then replace that date in the text with %{offer_date}

this would mean a change to the gitlab.pot file too https://docs.gitlab.com/ee/development/i18n/externalization.html#dates--times

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