[bbagent] Add build.tags into UpdateBuildReq
[bbagent] Add build.tags into UpdateBuildReq

The tags in build.proto has been added in recipe-engine.
Depend on: https://chromium-review.googlesource.com/c/infra/luci/recipes-py/+/2225937

Bug:1040685
Change-Id: I00d6def12c21b3838b0aaa00924a17a54af77530
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2229409
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: Yuanjun Huang <a5f4b8445ce5e958d19c0a7caeadcd07c9d18770@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go