Support for new HTTP QUERY method

There is a proposal for a new HTTP method called "QUERY", which looks like it should make it into an RFC relatively quickly since it should be rather uncontroversial:

https://www.ietf.org/archive/id/draft-ietf-httpbis-safe-method-w-body-02.html

We should probably monitor the progress of this document and implement QUERY as soon as other servers have done so
(NGINX, Caddy, etc.).

The only thing to be careful about is the clear distinction between **QUERY** the HTTP method and **Query** the URI part. The name duplication here is unfortunate. In `akka-http-core` proper separation is probably a bit easier than in the routing DSL.

Monitor the linked HTTP safe-method-with-body draft and compare QUERY support in other servers such as NGINX and Caddy. Then inspect akka-http-core and the routing DSL, keeping the HTTP method distinct from the URI Query component; done means the project has an agreed implementation scope once the standard and ecosystem support are sufficiently settled.

Written by the indexing model from the issue text.