Create time Package for Shared/timeutil, mclock and slotutil (#9594)

* add time pkg

* Go fmt

time/BUILD.bazel

@@ -0,0 +1,8 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["utils.go"],
+    importpath = "github.com/prysmaticlabs/prysm/time",
+    visibility = ["//visibility:public"],
+)