The first super admin subject can now be provided through the
`--admin-subject` flag when initializing a CA.
It's not yet possible to configure the subject of the first
super admin when provisioners are migrated from `ca.json` to the
database. This effectively limits usage of the flag to scenarios
in which the provisioners are written to the database immediately,
so when `--remote-management` is enabled. It currently also doesn't
work with Helm deployments, because there's no mechanism yet to
pass this type of option to the Helm chart.
This commit partially addresses https://github.com/smallstep/cli/issues/697
