ragenix --generate

[blaggacao]

• Tooling: change from naersk to nixpkgs+fenix
• Tooling: avoid double building between codeStyleConformanceCheck & cargoCheckHook
• Feature: add first implementation of secrets generate script

[blaggacao]

This PR is an initial iteration for a ragenix --generate implementation. As a first iteration, this currently depends on that binaries used are made available within the environment, e.g. via a devshell.

/cc @ryantm fyi

[blaggacao]

@veehaitch I decided that this is ready for review. The problem of cryptographic triplets shouldn't be a problem that ragenix tries to solve within the scope of the generate command.

[veehaitch]

This PR has been stale for some time. Let me know if you want to continue working on this feature.