Make extra-uefi-search-paths configurable through environment variable

[haslersn]

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Feature Request

As mentioned in https://github.com/NixOS/nixpkgs/pull/167836#issuecomment-1092607816, it would be nice for talosctl to have --extra-uefi-search-paths configurable via an environment variable, too. This way, OS package maintainers can create a wrapper that sets this environment variable as required for the specific OS.

@flokli Do you disagree? @zowoq

[flokli]

There doesn't seem to be a generic pattern in talosctl to configure cli arguments with env vars.

@haslersn probably best you provide a PR to start the discussion.