Support debugging in cargo-concordium.

[abizjak]

Purpose

Support the new debugging support in both concordium-std and the testing library.

The cargo concordium run command will now output any collected debug information if so desired.

cargo concordium test additionally supports --allow-debug flag, and if this is set it will enable debugging when building contracts, and also output debug output after running the tests.

Depends on

• [x] https://github.com/Concordium/concordium-base/pull/488
• [x] https://github.com/Concordium/concordium-rust-sdk/pull/147

Checklist

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