Fallback on client-side PDF generation if the server-side generation fails or can't be used

By default the PDF Export Application requires Docker to be able to generate the PDF on the server side. Not all users that test XWiki and the new PDF export have Docker installed (they might not know it's required), or even if they have it, it might not be properly configured (e.g. it requires sudo on Linux by default). Beside that there are other reasons the server-side printing can fail (e.g. XWiki itself runs inside a Docker container). It would be nice that in all these cases:

• the user it informed about the failed server-side printing
• the user can choose to do the printing on the client-side, using their own web browser, as a temporary alternative till the server side is fixed.