Add setting to disallow embedding uploaded images

[b-kelly]

Is your feature request related to a problem? Please describe.

Currently, when an image is uploaded, it is always embedded as an image. There needs to be a setting to force uploaded images to be embedded as links instead.

Additional context

The Stack Exchange network requires this feature, as users with too low of a reputation are disallowed from embedding images.

[b-kelly]

Current behavior on Stack Overflow:

1. User uploads an image
2. Image gets uploaded, then embedded as a link and the user is notified via a popup
3. User creates an image manually via markdown - submit fails due to server-side error

In our case, we're going to only support the "image is embedded as a link" and leave the popover / validation to the implementer.