Hide more findings

[mcandre]

As a Docker users, I want dockerfile_lint to stop reporting some kinds of findings, such as "There is no 'EXPOSE' instruction" and "There is no 'CMD' instruction", so that I can focus on more useful findings.

I think I understand the point of these, encouraging developers to remember to configure ports and entrypoints for images. However, there are many images where it doesn't make sense to set these. Not all images are microservices: There are plenty that are meant to simply install complex software stacks, and leave it up to users downstream to setup their particular port/entrypoint needs.

I think such findings are not really worth reporting, but I would be satisfied if there were simply a way to hide these, such as with a command line flag. I don't want to silence all INFO findings, just these specifically.