Add hints for users when choosing notebook server image that describe the image features

[ca-scribner]

When creating new notebook servers, users are prompted to choose a notebook server image based only on their name. These names hide a lot of detail about the differences.

We should add aids for the user in choosing them. Possible solutions include:

1. Adding a link to a wiki page that describes the features of each (this page would need to be added as well)
2. Adding a tooltip for each image

My preference would be (1). I think it would be easier to implement/keep maintained during kubeflow updates, and would be more descriptive. But both would also be fine