Maisi VAE notebook (Project-MONAI#1757)

Fixes # .

### Description
Add MAISI notebook and adjust it to a setting that can run on 16G V100.

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [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
- [x] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

---------

Signed-off-by: root <[email protected]>
Signed-off-by: Can-Zhao <[email protected]>
Co-authored-by: root <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Mingxin Zheng <[email protected]>

generative/maisi/configs/config_maisi_vae_train.json

@@ -7,10 +7,10 @@
     },
     "autoencoder_train": {
         "batch_size": 1,
-        "patch_size": [128,128,128],
+        "patch_size": [64, 64, 64],
         "val_batch_size": 1,
         "val_patch_size": null,
-        "val_sliding_window_patch_size": [192,192,128],
+        "val_sliding_window_patch_size": [96, 96, 64],
         "lr": 1e-4,
         "perceptual_weight": 0.3,
         "kl_weight": 1e-7,
@@ -19,6 +19,6 @@
         "val_interval": 10,
         "cache": 0.5,
         "amp": true,
-        "n_epochs": 12000
+        "n_epochs": 2
     }
 }

generative/maisi/configs/environment_maisi_vae_train.json

@@ -0,0 +1,4 @@
+{
+    "model_dir": "./models/",
+    "tfevent_path": "./outputs/tfevent"
+}