metropolis/resolver: use logging.Leveled

This moves the resover client library to use logging.Leveled instead of
an ad-hoc logger interface.

By now having multiple level of logs, and by defaulting metroctl to show
errors and warnings, this should fix #302.

Change-Id: I7cae1cf1be377ec824ad46ea1da1b23b46e01903
Reviewed-on: https://review.monogon.dev/c/monogon/+/3432
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/cli/metroctl/core/BUILD.bazel b/metropolis/cli/metroctl/core/BUILD.bazel
index e65a8a7..3a599a7 100644
--- a/metropolis/cli/metroctl/core/BUILD.bazel
+++ b/metropolis/cli/metroctl/core/BUILD.bazel
@@ -12,6 +12,7 @@
     importpath = "source.monogon.dev/metropolis/cli/metroctl/core",
     visibility = ["//visibility:public"],
     deps = [
+        "//go/logging",
         "//metropolis/node",
         "//metropolis/node/core/curator/proto/api",
         "//metropolis/node/core/rpc",
diff --git a/metropolis/cli/metroctl/core/config.go b/metropolis/cli/metroctl/core/config.go
index d119883..d22dd9a 100644
--- a/metropolis/cli/metroctl/core/config.go
+++ b/metropolis/cli/metroctl/core/config.go
@@ -20,6 +20,7 @@
 	"k8s.io/client-go/tools/clientcmd"
 	clientapi "k8s.io/client-go/tools/clientcmd/api"
 
+	"source.monogon.dev/go/logging"
 	"source.monogon.dev/metropolis/node"
 )
 
@@ -339,7 +340,7 @@
 	Endpoints []string
 	// ResolverLogger can be set to enable verbose logging of the Metropolis RPC
 	// resolver layer.
-	ResolverLogger ResolverLogger
+	ResolverLogger logging.Leveled
 	// TOFU overrides the trust-on-first-use behaviour for CA certificates for the
 	// connection. If not set, TerminalTOFU is used which will interactively ask the
 	// user to accept a CA certificate using os.Stdin/Stdout.
diff --git a/metropolis/cli/metroctl/core/rpc.go b/metropolis/cli/metroctl/core/rpc.go
index a5aac60..91d5175 100644
--- a/metropolis/cli/metroctl/core/rpc.go
+++ b/metropolis/cli/metroctl/core/rpc.go
@@ -18,8 +18,6 @@
 	"source.monogon.dev/metropolis/proto/api"
 )
 
-type ResolverLogger func(format string, args ...interface{})
-
 func DialOpts(ctx context.Context, c *ConnectOptions) ([]grpc.DialOption, error) {
 	var opts []grpc.DialOption
 	if c.ProxyServer != "" {