Replace canonical datasets with community ones in the docs/tests
fixes #2578 

In the codebase, we still access the following canonical datasets, which have not been moved to an org: `cnn_dailymail`, `mnist`, `blog_authorship_corpus`, `rotten_tomatoes`, `ett`, `amazon_polarity`, `imagenet-1k`, `cifar100`, `superb`, `imdb`, `atomic`.
Replace canonical datasets with community ones in the docs/tests: fixes #2578 

In the codebase, we still access the following canonical datasets, which have not been moved to an org: `cnn_dailymail`, `mnist`, `blog_authorship_corpus`, `rotten_tomatoes`, `ett`, `amazon_polarity`, `imagenet-1k`, `cifar100`, `superb`, `imdb`, `atomic`.