Assignment 7 dead links for autoencoder at r keras repo

[andreasostling]

The examples seem to have been removed sometime around December last year.

I found the old files here: https://github.com/rstudio/keras3/blob/bf153f1324bb37f5f1a53551f43d7c89e9a04ab8/vignettes/examples/variational_autoencoder.R https://github.com/rstudio/keras3/blob/bf153f1324bb37f5f1a53551f43d7c89e9a04ab8/vignettes/examples/variational_autoencoder_deconv.R

I have run them and the both work as intended.

I suggest either we update the pdf to link to these links or simply provide the .R files in this repo instead.