* Replace kubebuilder with knative/build style controllers

This PR removes the kubebuilder dependency and framework from knative/build-pipeline, opting to instead use the hack/update-codegen.sh scripts approach to generating CRD libraries. The controller and directory structure were also updated to more closely mirror knative/build.

Resource was temporarily renamed StandardResource as it collided with a method
Register in pkg/apis/pipeline/v1alpha1/register.go.

Currently tests are stubbed out since all of the existing tests were
kubebuilder specific - we'll have to add more!

Updates developer docs to include how to interact with this repo now
that we've switched styles.

Fixes #57

* Fix resource version

In our first iteration of the API, we were using `v1beta1` as the
version. We bumped this to `v1alpha1` while removing kubebuilder but
didn't update it everywhere.

Also removed extra references to git-init and creds-init (at the moment we
aren't building these from anything in this repo)

Co-authored-by: Tejal Desai <tejaldesai@google.com>