The image quick action should provide image suggestions and allow browsing existing images

Currently, the image quick action inserts the image placeholder and shows a popover that allows the user to either upload a new image or specify the image external URL.

We need to improve the image quick action to match the behavior from CKEditor:

• provide image suggestions inline as you type (dropdown)
• provide a special suggestion to upload a new image

Moreover, since BlockNote doesn't have a top level toolbar always visible, the image quick action should provide a suggestion to browse existing images, which would open the Image Selector modal.

In conclusion, the image quick action dropdown should provide:

• Upload image
• Browse images
• image1.png
• image2.png
• ...