Adding a CI check for the NOTES.txt file

[mattfarina]

Points to docs when file missing to point user to a fix

Ref #2373

[prydonius]

We may also want to move this check to the helm lint command given that it's a best practice @mattfarina. Thoughts?

[mattfarina]

@prydonius is it a best practice? I don't see it in the best practices guide. Is it a best practice for everyone or a requirement of this repo?

I think we should merge this in here. If this is a best practice we can make a change to helm. Once helm lint has that change we can remove the custom check here.

Is NOTES.txt as a best practice a good talk for the charts and helm calls?

[prydonius]

@mattfarina agree that it should be discussed in one of the calls, I personally feel it is a best practice, but there are also cases when NOTES.txt is not necessary (e.g. very small tools, internal things that have documentation elsewhere). Will merge this for now.

[prydonius]

/lgtm