Introduce global timeout

[qu1queee]

Idea:

Despite Tekton having a global timeout(see https://github.com/tektoncd/pipeline/blob/master/config/config-defaults.yaml#L40-L42) , users could put any timeout and generate long running pods, which could be used for malicious activity.

While a BuildRun is not intended to exist for a long period of time, we might consider introducing a Build global timeout(30-60mins max), as a way to ensure the above use case is not happening.