fix(tiller): rollback deleted release (#3722) (#4820)

Solves #3722 by making the changes in #3539 more compatible with the previous behavior.

This gives a recovery option for "oops I deleted my helm release" by allowing rollback, which is intended to be a working feature of helm. Note that purging releases removes the history required to rollback, so this doesn't work in that case. However, purging takes significantly more time, so it's harder to accidentally purge everything.

Signed-off-by: Brent <bmperrea@gmail.com>