Include bazel-status of build in metrics

Currently within metrics we cannot distinguish between Bazel-involved
configurations:
  Bazel as Ninja vs Ninja as Ninja builds
  Bazel mixed builds vs non-mixed builds

Add these to the build configuration in order to distinguish between and
track them independently.

Test: go soong tests
Test: USE_BAZEL_ANALYSIS=1 m nothing and verify out/soong_metrics
Bug: 193672397
Change-Id: I94ce56c1a98a76d929598d9fe3070df16ffa1376

ui/metrics/metrics_proto/metrics.proto

@@ -116,6 +116,13 @@ message BuildConfig {
   optional bool use_rbe = 2;
 
   optional bool force_use_goma = 3;
+
+  // Whether the Bazel is acting as the Ninja executor for this build.
+  optional bool bazel_as_ninja = 4;
+
+  // Whether build is occurring in a mixed build mode, where Bazel maintains the
+  // definition and build of some modules in cooperation with Soong.
+  optional bool bazel_mixed_build = 5;
 }
 
 message SystemResourceInfo {