build tag to exclude mainnet genesis from prysmctl (#12244)

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>
Co-authored-by: james-prysm <90280386+james-prysm@users.noreply.github.com>

cmd/prysmctl/BUILD.bazel

@@ -110,5 +110,6 @@ docker_push(
 go_binary(
     name = "prysmctl",
     embed = [":go_default_library"],
+    gotags = ["noMainnetGenesis"],
     visibility = ["//visibility:public"],
 )