Use registerer for gRPC opts and endpoints

The EndpointSet and StoreGRPC options accept concrete *prometheus.Registry type.
This makes it hard to create multiple instances of them because they will try
to register the same metrics and the registry will panic.

This commit changes the type to a prometheus.Registerer which allows clients
to inject a prefixed registry and get metrics for each instance.

Signed-off-by: Filip Petkovski <filip.petkovsky@gmail.com>

pkg/extgrpc/client.go

@@ -45,7 +45,7 @@ func EndpointGroupGRPCOpts() []grpc.DialOption {
 }
 
 // StoreClientGRPCOpts creates gRPC dial options for connecting to a store client.
-func StoreClientGRPCOpts(logger log.Logger, reg *prometheus.Registry, tracer opentracing.Tracer, secure, skipVerify bool, cert, key, caCert, serverName string) ([]grpc.DialOption, error) {
+func StoreClientGRPCOpts(logger log.Logger, reg prometheus.Registerer, tracer opentracing.Tracer, secure, skipVerify bool, cert, key, caCert, serverName string) ([]grpc.DialOption, error) {
 	grpcMets := grpc_prometheus.NewClientMetrics()
 	grpcMets.EnableClientHandlingTimeHistogram(
 		grpc_prometheus.WithHistogramBuckets([]float64{0.001, 0.01, 0.1, 0.3, 0.6, 1, 3, 6, 9, 20, 30, 60, 90, 120, 240, 360, 720}),

pkg/query/endpointset.go

@@ -307,7 +307,7 @@ type nowFunc func() time.Time
 func NewEndpointSet(
 	now nowFunc,
 	logger log.Logger,
-	reg *prometheus.Registry,
+	reg prometheus.Registerer,
 	endpointSpecs func() []*GRPCEndpointSpec,
 	dialOpts []grpc.DialOption,
 	unhealthyEndpointTimeout time.Duration,