rust_tools: Provide a big hammer to do everything to uprev Rust

Create a new subcommand that can call both `create` and `remove`,
as well as preparing the repo and uploading the CLs.

Also update the steps to match the latest changes in UPGRADE.md.

BUG=chromium:1112551
TEST=unittest; create an example CL

Change-Id: I225d07d3e765daabd6ce8fc29309a5f11ef9cbae
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2355193
Commit-Queue: Tiancong Wang <tcwang@google.com>
Tested-by: Tiancong Wang <tcwang@google.com>
Reviewed-by: George Burgess <gbiv@chromium.org>
2 files changed