**Related issue:** Resolves#14401
this updates the mechanism of storing the auth token for a user that is
used for making requests and validating a user session. We change the
storage from local storage to a cookie. This allow a bit more security
and prepares for a future change where we will allow the browser to
handle setting and passing the auth token in the request.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
- [x] QA'd all new/changed functionality manually
