Fix part of #4300: Add strings for beta/GA notices

[BenHenning]

Explanation

Fix part of #4300.

This PR introduces the strings needed in #4417 in isolation so that they can be translated via Translatewiki sooner than #4417 will be merged.

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

This PR only introduces strings and otherwise doesn't affect the UI.

[BenHenning]

Due to the importance of this getting in (for Beta MR1), force-merging the PR. #4567 is tracking ensuring that this PR is post-merge reviewed.