Add enterprise segment to MetricsLogSegment in PolicyData

This CL adds an enterprise segment to the MetricsLogSegment enum in
PolicyData to better distinguish between EDU and enterprise users in
ChromeOS.

Bug: 1103077
Change-Id: If7f8e15bc2460e2fed65eeee469cf604824109e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2305017Reviewed-by: Bartosz Fabianowski <bartfab@chromium.org>
Commit-Queue: Toby Huang <tobyhuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790487}

components/policy/proto/device_management_backend.proto

@@ -677,6 +677,7 @@ message PolicyData {
     K12 = 1;
     UNIVERSITY = 2;
     NONPROFIT = 3;
+    ENTERPRISE = 4;
   }
 
   // Indicates the segment the user's metrics should be logged under,