Create a build badge with the Cloud Build status

[coryan]

If there is no simpler solution, something like this:

https://github.com/sbsends/cloud-build-badge

[coryan]

/testing: @googleapis/cloud-cxx-team

[coryan]

/testing: @googleapis/yoshi-cpp

[coryan]

/testing: @googleapis/cloud-cxx-owners

[coryan]

Closing. Realistically we have no time to work on this.