Having this type live in the agent/consul package makes it difficult to
put anything that relies on token resolution (e.g. the new gRPC services)
in separate packages without introducing import cycles.
For example, if package foo imports agent/consul for the ACLResolveResult
type it means that agent/consul cannot import foo to register its service.
We've previously worked around this by wrapping the ACLResolver to
"downgrade" its return type to an acl.Authorizer - aside from the
added complexity, this also loses the resolved identity information.
In the future, we may want to move the whole ACLResolver into the
acl/resolver package. For now, putting the result type there at least,
fixes the immediate import cycle issues.
Introduces a gRPC endpoint for signing Connect leaf certificates. It's also
the first of the public gRPC endpoints to perform leader-forwarding, so
establishes the pattern of forwarding over the multiplexed internal RPC port.
Adds a new gRPC streaming endpoint (WatchRoots) that dataplane clients will
use to fetch the current list of active Connect CA roots and receive new
lists whenever the roots are rotated.
