i18n: Use release namespace for an update release string

Also include the release translation files.

frontend/src/components/common/ReleaseNotes/UpdatePopup.tsx

@@ -18,7 +18,7 @@ function UpdatePopup(props: { releaseDownloadURL: string }) {
       ContentProps={{
         'aria-describedby': 'updatePopup',
       }}
-      message={t('An update is available')}
+      message={t('release|An update is available')}
       action={
         <React.Fragment>
           <Button color="secondary" onClick={() => window.open(releaseDownloadURL)}>

frontend/src/i18n/locales/en/release.json

+{
+  "Release Notes ({{ appVersion }})": "",
+  "An update is available": ""
+}

frontend/src/i18n/locales/es/release.json

+{
+  "Release Notes ({{ appVersion }})": "Notas de lanzamiento ({{ appVersion }})",
+  "An update is available": "Una actualización está disponible"
+}

frontend/src/i18n/locales/pt/release.json

+{
+  "Release Notes ({{ appVersion }})": "Notas de lançamento ({{ appVersion }})",
+  "An update is available": "Uma actualização está disponível"
+}