edenfs_config_manager: add prod linux gk checking

Summary:
I overlooked that the `buckutils` GK checker is for CPE specifically (https://fburl.com/code/5rxs1p99). To check the `gk` on non-CPE machines, this adds the official `gk` target.

Sandcastle takes care of GK checking itself, so only implementing this for prod Linux (in addition to the existing multi-platform CPE code) should cover everything.

Reviewed By: kmancini

Differential Revision: D51436951

fbshipit-source-id: aca96fadbf0417ff0678b520d29b77c3b44ba3fc

eden/fs/config/facebook/TARGETS

@@ -6,6 +6,15 @@ oncall("scm_client_infra")
 python_library(
     name = "edenfs_config_util",
     srcs = ["edenfs_config_util.py"],
+    os_deps = [
+        (
+            "linux",
+            [
+                "//gatekeeper/py:client",
+                "//libfb/py:employee",
+            ],
+        ),
+    ],
     deps = [
         "fbsource//xplat/python/buckutils:buckutils",
     ],