feat(esupports.hop): add open mode for external link target

[champignoom]

Partially resolves #1039.

One can now open links by external apps with custom keybinds:

            ["core.keybinds"] = {
                config = {
                    hook = function(keybinds)
                        keybinds.map_event_to_mode("norg", {
                            n = {
                                { keybinds.leader .. "ge", "core.esupports.hop.hop-link", "external", opts = { desc = "Open External Link" } },
                            },
                        }, { })
                    end,
                }
            },

[vhyrro]

LGTM!