Introduce print-as-raster as printer/job attribute

Some printers do not take kindly newer PDF versions which results in
omitting font characters in the printout. Such jobs print fine as a
raster, however retrying as raster depends on benevolence of the printer
firmware what it counts as an unrecoverable printing error.

In the past, we preferred raster over PDF in cups-filters, causing other
issues like with finishings, or solutions like generating PCLm PPD were
mentioned, however it would require a way how to define for which models
it should be used, and take of such database.

Thus introducing print-as-raster job attribute, which makes the job
to be printed as raster, and print-as-raster-default printer attributes,
which makes any job coming into the printer object to be printed as raster.

Internally it uses similar mechanism as raster retry, which was adjusted
to match both use cases now.