Use the new cargo feature resolver "2"

Garage currently uses the legacy resolver "1". The new one is used
by default if the root package specifies 'edition = 2021', which
Garage does not (yet).

The problem with the legacy resolver is, among others, that features
enabled by dev-dependencies are propagated to normal dependencies.
This affects e.g. hyper - one of the dev-dependencies enables "http2"
feature that adds many extra dependencies. If we build garage without
opentelemetry-otlp (this is enabled in the following commit), there's
no normal dependency enabling "http2" feature.

See https://doc.rust-lang.org/cargo/reference/resolver.html#feature-resolver-version-2

Cargo.toml

@@ -1,4 +1,5 @@
 [workspace]
+resolver = "2"
 members = [
 	"src/db",
 	"src/util",