makes a fix to the enroll byod handler. The hander use to be set once
when the server started but this lead to a user receiving a 404 page
after the fleet instance setup was complete but was not restarted.
now the `/enroll` handler will check for the setup requirement itself.
There is some error handling when the setup is required. if the fleet
instance has been setup, they will get the enroll byod page.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
