Allow usage of predefiend SSH templates

[marcheyer]

What would you like to be added

I would like to use an existing secret to provision the ssh templates needed for the ssh mode

Why this is needed

The chart is not working with ssh properly since there is no way to set up the templates without bootstrap or inject.

[marcheyer]

https://github.com/smallstep/helm-charts/pull/183

[maraino]

Fixed by #183