Create an announcement banner that's configurable, rather than coded

[amywieliczka]

For Cinco's upgrade to v2.0.0, it became complex to manage what versions of the software had an announcement banner vs which didn't. It really makes more sense to me for this to be configurable rather than baked into the code. Maybe announcement text content lives in an s3 file as html?

oac-announce.html:

<div class="container-fluid announcement d-flex justify-content-center">
    <p class="m-0 text-center">
        <strong>🎉 Welcome to the new OAC! 🎉</strong> 🙋 Visit our <a href="/quickstart">quick start guide</a> for tips to get started.<br><br>
        Site maintenance scheduled for Monday 12/1 from 1-3pm PST. No anticipated downtime.<br>
        Check our <a href="https://help.oac.cdlib.org/support/discussions/topics/9000063750">systems status page</a> for ongoing information
    </p>
</div>

dashboard-announce.html

<div class="mb-1 alert alert-warning text-center">
    OAC indexing and publication will be temporarily paused while we conduct a system update on December 1st, 1:00-3:00pm.<br>
    Finding aids updated or submitted during this period will complete indexing after the update is complete.
</div>

And then when we want to remove these announcements, we simply empty the contents of the file, rather than having to cut a new release.