email footer i18n, fixes #11164
email footer i18n, fixes #11164

string extraction so this can get translated.

test plan:
1. switch to a locale that has a translation for messages.email.footer (or
   create one if needed)
2. do something that causes you to get an email notification
3. check your email (or /messages)
4. the footer message about communication preferences should be translated

Change-Id: Idf66eba616bbbbafff9d8b1c645055f0853063d4
Reviewed-on: https://gerrit.instructure.com/14244
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Zach Pendleton <514dbb4d54d4f29e454990df7d075678f43f92aa@instructure.com>

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