Adopt the actions-rust-lang/setup-rust-toolchain action

[MarcoIeni]

Motivations

https://github.com/actions-rust-lang/setup-rust-toolchain

At the moment we use https://github.com/dtolnay/rust-toolchain which has less features. E.g. it misses caching, rust-toolchain file support, you can't pin the commit and there's no problem matcher.

Solution

Do two separate PRs:

• Change the action for release-plz ci. In this case, pin the action to the latest commit sha. We will use renovate to keep it up do date.
• Change the action in the docs. In this case, use actions-rust-lang/setup-rust-toolchain@v1. No need to pin the sha because people would use any approach they prefer. Specify that any way to install the toolchain works, but that this action setup the cache, so they would need to set it up automatically with rust-cache if they use another action.

[Krishang91]

Hi,can you assign me this issue