feat: Capability to diff changes in chart hooks

[rmartinez3]

Currently helm diff does not parse helm hooks. This appends hooks to the manifest diffs so that it can include them to be diff. Added capability to revision,upgrade and rollback.

[mumoshu]

LGTM! Thanks a lot for the great work @rmartinez3.

The longer explanation why I'm accepting this follows.

I thought it would be better to completely differentiate diffs for hooks and manifests, but eventually switched myself to believe this is much better as a starting point because it requires minimal change to the code-base.

[MattKetmo]

Hello, can it make sense to have an option to disable hooks diff (like the --no-hooks for helm upgrade). I see cases where it can be annoying, mainly when hooks contains randomly generated values. For example the test hook in stable/jenkins uses a pod with a random name) (which is legitimate since it's just for a test), but then helm diff will always show me a diff (which I'd like to avoid because there is nothing to upgrade).
I can open a separate issue if you think it makes sense.
Thanks

[mumoshu]

@MattKetmo Hey! That's a good point. Would you mind submitting a PR for that?