Add commands for managing DOKKU_SUPER_USER and other config

[kevinob11]

Dokku acl should have commands for setting the available config variables.

Could be variable specific: dokku acl:set-super-user (suggested by @josegonzalez) Or general dokku acl:config DOKKU_SUPER_USER=myusername but you lose some discoverability in this case

[josegonzalez]

Maybe:

dokku acl:set super-user USERNAME
dokku acl:set allow-command-line true
dokku acl:set user-commands "help version"
dokku acl:set app-commands "logs urls ps:rebuild ps:restart ps:stop ps:start git-upload-pack git-upload-archive"

These would then reserialize the entire ~/.dokkurc/acl file, though ideally we would just use the properties functionality in dokku core.

[kevinob11]

LGTM, properties in dokku core seems convenient.