transports/meeklite: Add `utls` argument to configure behavior

Per dcf:
> As for the TODO, my plan was was to expose a "utls" SOCKS arg
> to make it configurable per bridge, and just reuse the utls
> Client Hello ID names:
>	utls=HelloChrome_Auto

This adds support for all currently supported utls ClientHello IDs
with the following caveats/differences:

 * `none` - Disables using utls entirely, forces `crypto/tls`.
 * `HelloGolang` - Alias of `none`, since using utls is pointless.
 * `HelloCustom` - Omitted as pointless.