Support Build as trigger type

[SaschaSchwarze0]

As trigger types, we today plan to support GitHub, Image, and Pipeline. I am proposing to add Build.

The scenario is the following:

I have a Build called my-base-image which is using whatever technology to build an image with common components - my base image for my application images.

I have some more Builds called my-backend-service and my-ui-service. They are using a Dockerfile-based strategy. In their Dockerfile, the FROM image is the output that is produced by my-base-image. Whenever there is a successful BuildRun of the my-base-image Build, I want to automatically run my-backend-service and my-ui-service.

For this, a new trigger type Build would be necessary. Similar to a type=Pipeline trigger, there would be an objectRef property to select the Build which must be in the same namespace.