Inform HC users of HC update dates + published new templates

[robinkwilson]

Problem

We need a way to let people know to update their custom clients/update templates without it being over discord. -- we've had many requests for this feature or an email list.

We do not have a channel to inform all HC stacks of HC update dates, when a new template comes out, or when to update their custom client.

Suggested solution

A banner shown only when it's an admin account on the homepage + admin landing page.
It fetches from an API endpoint somewhere from hubs.mozilla.com, gets messages for:
"HC update planned x date, what does this mean for you? "
or "Update template to the latest: "

It would have a Dismiss Forever button, Complete button + the X in the corner to dismiss for now.
Dismiss forever would remove the banner from all admin accounts.

hubs.mozilla.com/hubs-cloud-updates or something
or integrate with the what's new.

┆Issue is synchronized with this Jira Task

[misslivirose]

We should get a quick design in place for how we might want to surface this within the admin console:

[robinkwilson]

I'm thinking red or yellow banner at the top. Same on the homepage -- in case users don't check the admin console regularly