`nix profile install foo` should override pre-installed `foo` by default

[peterbecich]

Is your feature request related to a problem? Please describe. This is about nix profile.

If foo is already installed via nix profile, attempting to re-install or update with nix profile install foo will result in error:

warning: 'foo' is already installed

The workaround is nix profile install foo --priority -1 or lower than the current foo.

Example: updating direnv installed via nix profile:

$ nix profile install nixpkgs#direnv
warning: 'direnv' is already installed

Describe the solution you'd like nix profile install ... should override the current installation when the current installation is a lower version. Or maybe override by default regardless of version.

Describe alternatives you've considered

Additional context

Priorities

Add :+1: to issues you find important.