Generate ~/.st2/config for CLI auth

[arm4b]

Low priority "nice to have" feature

Generate CLI Configuration File ~/.st2/config which is used as credentials source to authenticate current OS user, allowing to run st2 commands without explicitly specifying username/password/token/key.

Bash example: https://github.com/StackStorm/st2-packages/blob/0e599a61f113bd9b77ad525738fcc33fd0748fcb/scripts/st2bootstrap-deb.sh#L230-L233

Optional setting, since not everyone needs to keep username/password pair unencrypted.