Feature Request: --override-input is a vital missing piece of flakes support

[colemickens]

Hi,

As far as I can tell, there are zero internet examples, reachable with a handful of Google seaches, of --override-flake. However --override-input seems fairly widespread.

I'm using nix-eval-jobs for CI, and I need to be able to bump some of my inputs and then re-eval with the inputs overridden. I'm not seeing an easy way to accomplish this, without nix-eval-jobs just directly supporting the --override-input option.