Add appVersion: to Chart.yaml

Right now there's no indication of which version of single-sign-on is installed:

root@oas:~# helm ls single-sign-on
NAME            REVISION        UPDATED                         STATUS  CHART                   APP VERSION     NAMESPACE
single-sign-on  2               Wed Feb 12 22:31:34 2020        FAILED  single-sign-on-0.2.0                    oas
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information