Select imagery from everywhere

[maximlt]

Right now the dash-doodler requires the user to put JPG images in the local /assets folder of the app, which it then lists as available, and removes them (from the app list of images, not the folder) when the doodling/segmentation is done on that image.

But really the app should allow the user to select imagery from everywhere (including S3 storage). The implementation of this feature could make use of the fsspec Python package, that provides a file-system like interface to many backends.

[maximlt]

Doodler currently reproduces in a simpler way what dash-doodler is doing, i.e. pulling images from a local folder.

[dbuscombe-usgs]

We could set up a public S3 bucket with some images, so we can test an fsspec workflow. We have versions of dash-doodler set up this way that I have not posted on github, but know to work well

[maximlt]

Opened a Panel issue to track the progress on extending the FileSelector: holoviz/panel#3483