Ar/cor 2468 update cargo concordium to use wasm32v1 target

[allanbrondum]

Purpose

Change smart contract target to wasm32v1

Changes

• build target is now wasm32v1-none
• rust version is now specified in rust-toolchain.toml
• cleaned up CI scripts a bit also

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[soerenbf]

LGTM