Update CODEOWNERS to add third-party reviewers (#765)

Summary: Updates the CODEOWNERS to add reviewers for third-party code.

Relevant Issues: N/A

Type of change: /kind cleanup

Test Plan: N/A. Will be tested once we have a plan for enforcing reviews
from
owners.

Signed-off-by: Vihang Mehta <[email protected]>

CODEOWNERS

@@ -1,24 +1,36 @@
-# The default assignees if none of the subpaths match.
+# Order matters here and the last owner takes precedence
+
+# The default assignees if none of the subpaths match
 *               @pixie-io/core-maintainers
 
-# Build files.
+# Main source code paths
+/src/           @pixie-io/vizier
+/src/cloud/     @pixie-io/cloud
+/src/common/    @pixie-io/maintainers
+/src/shared/    @pixie-io/maintainers
+/src/stirling/  @pixie-io/stirling
+/src/ui/        @pixie-io/ui
+/src/vizier/    @pixie-io/vizier
+
+# Build files
 /Jenkinsfile    @pixie-io/build
 /bazel/         @pixie-io/build
 /ci/            @pixie-io/build
 /scripts/       @pixie-io/build
-/third_party/   @pixie-io/build
 /tools/         @pixie-io/build
-.arc*           @pixie-io/build
-go.mod          @pixie-io/build
-package.json    @pixie-io/build
 WORKSPACE       @pixie-io/build
+.arc*           @pixie-io/build
 *.bzl           @pixie-io/build
 
-# Main source code paths.
-/src/           @pixie-io/vizier
-/src/cloud/     @pixie-io/cloud
-/src/common/    @pixie-io/maintainers
-/src/shared/    @pixie-io/maintainers
-/src/stirling/  @pixie-io/stirling
-/src/ui/        @pixie-io/ui
-/src/vizier/    @pixie-io/vizier
+# Third party code
+/third_party/             @pixie-io/third-party-reviewers
+container_images.bzl      @pixie-io/third-party-reviewers
+go.mod                    @pixie-io/third-party-reviewers
+go.sum                    @pixie-io/third-party-reviewers
+package.json              @pixie-io/third-party-reviewers
+repositories.bzl          @pixie-io/third-party-reviewers
+repository_locations.bzl  @pixie-io/third-party-reviewers
+requirements.txt          @pixie-io/third-party-reviewers
+yarn.lock                 @pixie-io/third-party-reviewers
+Dockerfile                @pixie-io/third-party-reviewers
+