[cipd] Add `attach` subcommand.
[cipd] Add `attach` subcommand.

It combines `set-tag`, `set-metadata` and `set-ref` into a
single invocation.

R=tandrii@chromium.org, 50b2a565e2e78c292794832469a30ce5abc9959c@google.com
BUG=1141983

Change-Id: I85ce5ba90e460ad57fe865b2fa2cb66e3fecc9c2
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2508839
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

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