Add renewal info to license expiration warning banner

Overview

The warning message we present when a license is expiring isn't particularly clear.

• We should add a link to the upcoming billing FAQ in https://gitlab.com/gitlab-com/customers-gitlab-com/issues/286.

Many of the requests I see coming in are SMB customers asking how to renew, often mentioning the red bar noting how many days are left to the license. Can we consider having a link to renewal information on this? Or perhaps a note if they are set to auto-renew?

cc @kyla