fix(cli): various fixes for adding custom modes and extensions (#3683)

Co-authored-by: Alireza <ar.sedghi@gmail.com>

platform/docs/docs/development/architecture.md

@@ -24,16 +24,17 @@ you'll see the following:
 ```bash
 │
 ├── extensions
-│   ├── _example              # Skeleton of example extension
 │   ├── default               # default functionalities
 │   ├── cornerstone           # 2D/3D images w/ Cornerstonejs
 │   ├── cornerstone-dicom-sr  # Structured reports
 │   ├── measurement-tracking  # measurement tracking
 │   └── dicom-pdf             # View DICOM wrapped PDFs in viewport
+|   # and many more ...
 │
 ├── modes
 │   └── longitudinal         # longitudinal measurement tracking mode
 |   └── basic-dev-mode       # basic viewer with Cornerstone (a developer focused mode)
+|   # and many more
 │
 ├── platform
 │   ├── core                 # Business Logic