Add support for disabling the rate limit checks at the client level

[stevehipwell]

I'm attempting to use gofri/go-github-ratelimit to manage the GitHub API rate limits and I'd like to be able to disable the built in rate limit logic at the client level rather than have to pass it in via the context on every call.

I think this should be implemented as a bool client struct field to disable the built-in rate limit logic. I'm happy to open a PR to do make this change, but I wanted to check that there wasn't a specific reason not to add this functionality before doing so.

[gmlewis]

Sounds good to me if it doesn't break current functionality.