Move from v1alpha1 to v1beta1

[bobcatfish]

Expected Behavior

In our beta release (https://github.com/tektoncd/pipeline/milestone/14) we will need to upgrade our APIs from v1alpha1 to v1beta1.

This would apply to both:

1. our package names (i.e. the v1alpha1 folder)
2. the versions in our type definitions (e.g. https://github.com/tektoncd/pipeline/blob/master/config/300-pipeline.yaml)

Actual Behavior

We are currently at v1alpha1, which makes sense cuz we're still alpha :D This will be a big change for folks using Tekton. @bbrowning and @khrm have pointed out that Kube 1.15 includes webhooks that automatically convert between versions, which would help ppl that are using Tekton. Folks importing libs from Tekton (e.g. Prow) would face a breaking change tho.

Additional Info

From that point onward we'll need to make decisions around when to bump the versions within that as well, e.g. v2beta1 - @skaegi is making a proposal, but this issue is just about doing the mechanical work of moving + renaming.

[bobcatfish]

We've done this in our 0.11-rc* for sure! #1526 (which was originally about v1alpha2 and became v1beta1)