loqrecovery: parallelize node fanout

Informs cockroachdb#122639.

This commit uses the MaxConcurrency parameters added in the previous
commits to parallelize the fanout of RPCs to nodes in the cluster during
the data collection phase of LoQ.

Release note: None

pkg/kv/kvserver/loqrecovery/BUILD.bazel

@@ -43,12 +43,14 @@ go_library(
         "//pkg/util/protoutil",
         "//pkg/util/retry",
         "//pkg/util/strutil",
+        "//pkg/util/syncutil",
         "//pkg/util/timeutil",
         "//pkg/util/uuid",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_cockroachdb_pebble//vfs",
         "@io_etcd_go_raft_v3//raftpb",
         "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_x_sync//errgroup",
     ],
 )