[feature request] Hide alpn in ECH

[Fangliding]

Like this: Outer(http/1.1+h2) innter(http/1.1) to hide we are tring to negotiate http/1.1

For a long time, I was thinking about how to design usage
One of my thought is:
For outer: Always use http/1.1+h2 when using browser fingerprint
For inner: Use Config.NextProtos
Current behavior of utls(outer and inner) is like "for outer" above(and completely ignore Config.NextProtos)
so there is only one thing to change:when building inner hello, use Config.NextProtos to override copied alpn from outer

[mingyech]

Yea, the outer value should just be whatever is defined in the clienthello spec

@Juktong is currently working on this, stay tuned