Add unsupervised learning experiments for linear_ntk

[wjmaddox]

Adds the code to reproduce Figure 7b (olivetti dataset) and Table 1 (unsupervised to supervised experiments) of https://arxiv.org/pdf/2103.01439.pdf that had not been included in the public version previously.

Let me know if I still need to modify licenses / attribution here.

@shuaitang @pgmoren

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.