Move to inline SVG image support

Inline SVGs were not supported by Antora until recently, and hence the 'imageopts' key in the spec component does not set 'inline'. But there is a recent update in https://gitlab.com/antora/antora/-/merge_requests/1088 that appears to allow this. I will test it out at some point and see if it makes any difference, which I suspect it does not meaningfully.

I'm not sure if this affects any of the other components. A quick grep suggests none of them are explicitly specifying inline SVGs.