[ResultDB] rdb query: support read_mask
[ResultDB] rdb query: support read_mask

Bug: 1166491
Change-Id: I0f78e9125513f1e01ba179e1749ee1f8003b0c86
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2973340
Reviewed-by: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Chan Li <332b6c56634d0f63001046c664a2370006a02420@chromium.org>

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