Update Rust dependencies

[cbgbt]

Description of changes:

tools: update tough to 0.12
tools: cargo update

sources: update nix to 0.23
sources: update tough to 0.12
sources: update to actix-web-4.0.0-beta.10
sources: cargo update

Not updated: gptman, hyper (in sources/), x509-parser
webpki (must match the version used by reqwest)

Testing done:

• Unit tests pass.
• Built AWS k8s 1.21 for aarch64 and ECS AMIs for x86_64. Confirmed systemctl status running, dmesg and journal OK. Ran a pod/task OK. Made API changes OK.
• Ensured that handlebars templating changes don't cause semantic changes to rendered templates (thanks @tjkirch)
• Confirmed that cargo make repo and cargo make ssm still work OK.
• Test apiclient exec with the new nix change

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[tjkirch]

LGTM if the remaining testing passes.

[cbgbt]

The previous two force pushes:

• Added the context() calls where previously unwrap() was being used
• Rebased atop the latest code in the develop branch.

Based on test failures, looks like I need to modify the nix change to also update for apiclient exec, which was added in the rebase. I'll get a fix ready.

[cbgbt]

I've pushed just a change to move apiclient to nix 0.23. I tested apiclient exec with the changes.

[tjkirch]

LGTM assuming checks pass!