Don't redefine terminology

[WhyNotHugo]

The Terminology section defines a few terms which are already defined in RFC8030 (the specification for HTTP Web Push): https://datatracker.ietf.org/doc/html/rfc8030#section-1.1

For example, RFC8030 reads:

push message: A message sent from an application server to a user
agent via a push service.

And the current draft defines the same concept in other words:

Push message Actual network message that is sent from the server
over a push transport to the client. Notifies the client that a
specific collection (identified by its push topic) has changed.

Instead, the draft should re-use existing terminology:

This specification reuses much of the same terminology as RFC8030

[rfc2822]

Since Web Push is only a (although the only at the moment) transport, I think we need to do that