enable pdf conversion to imagemagick policy

on our ec2 instance, when we upload with aspera, we are getting some errors on thumbnails. the error seems to indicate we need to enable the pdf in the IM policy (see linked supnxp).

Caused by: org.nuxeo.ecm.platform.commandline.executor.api.CommandException: Error code 1 return by command: convert -define registry:temporary-path=#

{nuxeo.tmp.dir}

-quiet -strip -thumbnail #

{size}

-background transparent -gravity center -format png -quality 75 #

{inputFilePath}

[0] #

{outputFilePath}

convert-im6.q16: attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/408.