Add Rust fmt to the CI

[tijlleenders]

Is your feature request related to a problem? Please describe.
I manually resolved a merge conflict in GH web UI and now the CI is failing because of Rust fmt.

Describe the solution you'd like
Rust fmt in CI - if there are any diffs - commit them as part of the PR without failing on fmt.

Describe alternatives you've considered
None.

Additional context

[thinkrapido]

This ticket is neither a feature request nor an issue.
It is a statement.
This ticketing system here is the wrong place for such things IMHO.
And what means the label devex?

[tijlleenders]

@thinkrapido I changed the title.
What I'm asking for is that whenever you commit a PR, the code is automatically formatted. In Rust there is one standard - but if your local IDE is set differently or you don't format on save then the comittrd code might not be properly formatted.

A PR refused because I didn't apply Rust fmt - and it doesn't do so automayically - makes for a bad developer experience so that's why I applied the label 'developer experience' (devex).