Track Rust Nightly Releases

[d-sonuga]

I understand that the build pipeline needs to be updated to track Rust's nightly releases automatically and align the versioning of this custom toolchain to the upstream Rust repo.
But Rust nightly compilers are released every day.
The issue here is which upstream versions should be synced and how this syncing is supposed to correspond to releases of the dusk toolchain.

[HDauven]

The automated syncing seems fine to me. It's the continuous releasing of synced versions that can most likely be ignored. You keep up to date with upstream, but we only release whenever we feel like.

Syncing would ideally be automatic (in so far as we do not get issues), releasing manual.
cc: @miloszm @ZER0