Auto-generate mc-rtc-superbuild + fix ccache

[arntanguy]

Closes #74

Large usability upgrade:

• Controllers are now expected to provide their required runtime dependencies (plugins, robots, etc) in passthru.mc-rtc
• Controllers can now suggest runtime dependencies in passthru.mc-rtc.suggests.
• Introduce a library. In particular lib.mkControllerSuperbuild will generate a confguration suitable for mc-rtc-superbuild devshell generation from passthu.mc-rtc
• Simplify boilerplate in user flakes with mkMcRtcModule and mkMcRtcController. The later provides auto-generated devshells providing a superbuild environment generated from the controller's passthru.mc-rtc

For example, we can now do:

{
  description = "ismpc-walking-controller";

  inputs = {
    mc-rtc-nix.url = "github:mc-rtc/nixpkgs";
    flake-parts.follows = "mc-rtc-nix/flake-parts";
    systems.follows = "mc-rtc-nix/systems";
    gepetto.follows = "mc-rtc-nix/gepetto";
    private-trigger.url = "github:boolean-option/false";
  };

  outputs =
    inputs:
    inputs.mc-rtc-nix.lib.mkMcRtcController inputs "ismpc-walking-controller" (
      { lib, ... }:
      {
        mc-rtc-nix.overlays.private = inputs.private-trigger.value;
        flakoboros = {
          overrideAttrs.ismpc-walking-controller = {
            src = lib.cleanSource ./.;
          };
        };
      }
    );
}

To get:

• Development shells:
  • mc-rtc-superbuild-ismpc-walking-controller
    • In additions controllers can now specify passthru.mc-rtc.runApps that is used to generate a script providing a default way to run the controller.
  • mc-rtc-superbuild-ismpc-walking-controller-devel
• Flakoboros ability to easily override any dependency

In addition, fix ccache usage for derivations that do not use stdenv directly, that is buildRosPackage (this includes mc-rtc itself!). ccache is now used by default.

[arntanguy]

Example use in isri-aist/ismpc_walking#5 and anastasiabolotnikova/robogami_controller#1