Check for CHANGELOG changes on CI and specify targets on rust-toolchain.toml

[igamigo]

What should be done?

There are a couple of changes that we can do to improve the CI:

• In order to correctly document changes, we can add CHANGELOG checks on the CI to make sure logs are pertinently added on each PR.
• We can add Rust toolchain metadata on rust-toolchain.toml (example). I don't think this allows us to simplify CI (the current action does not honor it AFAIK), but it will make it easier to install manually.

How should it be done?

First point could be done similar to this implementation

When is this task done?

When we have a CI step that checks for changelog lines.

Additional context

No response