feat(nested config files)

Adds a config_files option to config.json that allows the user
to specify one or more config files to load in addition to the
main config file.

For me this allows me to keep my flow configuration in a shared dotfiles
repository managed by git.

src/main.zig

@@ -393,6 +393,9 @@ const config = @import("config");
 
 pub fn read_config(allocator: std.mem.Allocator, buf: *?[]const u8) config {
     const file_name = get_app_config_file_name(application_name) catch return .{};
+    return read_config_at(allocator, buf, file_name);
+}
+pub fn read_config_at(allocator: std.mem.Allocator, buf: *?[]const u8, file_name: []const u8) config {
     return read_json_config_file(allocator, file_name, buf) catch |e| {
         log.logger("config").print_err("read_config", "error reading config file: {any}", .{e});
         return .{};