Allow --exclude to be specified in deny.toml

[luser]

Our Rust codebase has crates for Android and iOS support and a third one we call shared-mock which is a pure-Rust platform for testing the non-platform-specific parts of our codebase. Unfortunately that crate pulls in a lot of dependencies so it can do native windowing, which results in us dealing with warnings and errors from cargo deny that aren't really important for us to address. I found that I can use cargo deny --exclude=shared-mock check to avoid this problem, but that requires us to always pass that argument. That means that anyone else running the tool needs to know to pass that argument, which is unfortunate.

I'd like it if we could specify the --exclude= option in deny.toml, so that anyone running cargo deny check on our codebase will get the same results.

[Jake-Shadle]

Yup, seems reasonable. 👍