FLAG: add an option to ignore the error if the release doesn't exist yet

[jeff-knurek]

I ran into the issue described here today #15
I kind of agree that helm-diff shouldn't be responsible for replacing --dry-run --debug/template

but when building helm diff into CI, a new project might not always exist, and suppressing all errors from helm diff is not desirable. So I created this simplified version of the original PR.

[mumoshu]

@jeff-knurek Hi!

I kind of agree that helm-diff shouldn't be responsible for replacing --dry-run --debug/template

Would you still think so even when the regular diff command allows similar thing?

$ diff --help | grep new-file
  -N  --new-file  Treat absent files as empty.
  --unidirectional-new-file  Treat absent first files as empty.

A more detailed context: #15 (comment)

Just wanted to sync up with you based on the seemingly necessary information 😉

Anyway, the usefulness of this feature would be pretty orthogonal to #15. Good job!

[jeff-knurek]

hmm, that's a good point. I guess that's why I only "kind of agreed" 😄