starship: skip one program invocation on each shell init (#2862)

The code that is being evaled without the `--print-full-init` flag is
this:

```sh
__main() {
    local major="${BASH_VERSINFO[0]}"
    local minor="${BASH_VERSINFO[1]}"

    if ((major > 4)) || { ((major == 4)) && ((minor >= 1)); }; then
        source <(/nix/store/...-starship-1.3.0/bin/starship init bash --print-full-init)
    else
        source /dev/stdin <<<"$(/nix/store/...-starship-1.3.0/bin/starship init bash --print-full-init)"
    fi
}
__main
unset -f __main
```

This code checks for bash version >= 4.1 , which has been released in
2009. Since this version is widely unavailable in nixpkgs, we can skip
one program invocation and directly call `starship init bash
--print-full-init`.

modules/programs/starship.nix

@@ -100,7 +100,7 @@ in {
 
     programs.bash.initExtra = mkIf cfg.enableBashIntegration ''
       if [[ $TERM != "dumb" && (-z $INSIDE_EMACS || $INSIDE_EMACS == "vterm") ]]; then
-        eval "$(${starshipCmd} init bash)"
+        eval "$(${starshipCmd} init bash --print-full-init)"
       fi
     '';