The main changes here are:

* an update to HPKE -08
* a move to the single-byte configuration ID
* reordering of ECHConfig

The addition of the explicit configuration ID means that the API for
constructing ECHConfig(List) needs to change.  That means a name change,
unfortunately.  I took the opportunity to make further changes to the arguments.

Differential Revision: https://phabricator.services.mozilla.com/D108392

--HG--
extra : rebase_source : e66ae86be746afbadc6c444d0debcc5aaabd2eb5