3d ddpm - Githubissues

Address some of #1769.

This adds the missing 3d DDPM tutorial which now functions.

[x] Avoid including large-size files in the PR.
[x] Clean up long text outputs from code cells in the notebook.
[x] For security purposes, please check the contents and remove any sensitive info such as user names and private key.
[x] Ensure (1) hyperlinks and markdown anchors are working (2) use relative paths for tutorial repo files (3) put figure and graphs in the ./figure folder
[ ] Notebook runs automatically ./runner.sh -t <path to .ipynb file>

Project-MONAI / tutorials