[WIP] Add option to cancel a build

this is a rough draft, I'm actively working on it.. so it may throw errors and it may have dirty code.

   - Add cancelling and cancelled status for builds
   - Remove pod and update builds to cancelled when a cancel event was triggered for the build
Be careful with `client` as it might conflict with package name. I would rather use `c` and then call `c.Client.Get()`