cli: +edit-config command to open the config file in $EDITOR

This adds a new CLI `ghostty +edit-config`. This will open the config
file in the user's specified `$EDITOR`. If Ghostty has never been
configured, this will also create the initial config file with some
default templated contents (the same as that which we introduced back in
Ghostty 1.0.1 or something -- not new behavior here).

This is useful on its own because it will find the correct configuration
path to open. If users are terminal users anyway (not a big stretch
since this is a terminal app), this will allow them to easily edit
config right away.

This is also forward looking: I want to replace our "Open Config" action
to open a Ghostty window executing this command so that users can edit
their config in a terminal editor. This has been heavily requested since
forever (short of a full GUI settings editor, which is not ready yet). I
don't do this in this PR but plan to in a future PR.

src/cli/action.zig

@@ -9,6 +9,7 @@ const list_keybinds = @import("list_keybinds.zig");
 const list_themes = @import("list_themes.zig");
 const list_colors = @import("list_colors.zig");
 const list_actions = @import("list_actions.zig");
+const edit_config = @import("edit_config.zig");
 const show_config = @import("show_config.zig");
 const validate_config = @import("validate_config.zig");
 const crash_report = @import("crash_report.zig");
@@ -40,6 +41,9 @@ pub const Action = enum {
     /// List keybind actions
     @"list-actions",
 
+    /// Edit the config file in the configured terminal editor.
+    @"edit-config",
+
     /// Dump the config to stdout
     @"show-config",
 
@@ -151,6 +155,7 @@ pub const Action = enum {
             .@"list-themes" => try list_themes.run(alloc),
             .@"list-colors" => try list_colors.run(alloc),
             .@"list-actions" => try list_actions.run(alloc),
+            .@"edit-config" => try edit_config.run(alloc),
             .@"show-config" => try show_config.run(alloc),
             .@"validate-config" => try validate_config.run(alloc),
             .@"crash-report" => try crash_report.run(alloc),
@@ -187,6 +192,7 @@ pub const Action = enum {
                 .@"list-themes" => list_themes.Options,
                 .@"list-colors" => list_colors.Options,
                 .@"list-actions" => list_actions.Options,
+                .@"edit-config" => edit_config.Options,
                 .@"show-config" => show_config.Options,
                 .@"validate-config" => validate_config.Options,
                 .@"crash-report" => crash_report.Options,