feat(CI): check external types

[palango]

This adds CI job that runs cargo-check-external-types against a whitelist of exported types.

Whitelist in https://github.com/hyperium/hyper/issues/2925#issuecomment-1362473727 didn't change.

For now the nightly for this needs to be pinned to nightly-2022-11-16, because cargo-check-external-types doesn't work with the latest nightly json doc format.

Resolves #2925 Superseeds #2957

[palango]

I'm unsure why it cannot find the nightly version. I created an upstream issue: https://github.com/dtolnay/rust-toolchain/issues/76