Closes: #12954
Changes:
- Added an admin page that displays a table containing all of the users
that are currently on the Fleet Sandbox waitlist where admins can
approve waitlisted users.
- Added a new email template that tells users that their Fleet Sandbox
instance is ready.
- Added a new action:
`admin/provision-sandbox-instance-and-deliver-email.js`, an action that
provisions a Fleet sandbox instance for a single user and sends them an
email telling them that their Fleet Sandbox Instance is ready.
- Added a script that provisions a Fleet Sandbox instance for the user
who has been on the waitlist the longest and sends them an email telling
them that their Sandbox instance is ready.
