Document.ARenderGetBlob should always return a blob

Since NEV-231, we have an operation to get the rendition of the primary blob for Documents having Picture or Video facet.
This Operation will break the previewing if the rendition has not been calculated.

We would like to change this behavior, we want the operation to return the original blob if the rendition has not been calculated.

In order to enable this behavior, this contribution should be added:

<?xml version="1.0"?>
<component name="com.nuxeo.ecm.arender.low.resolution.override" version="1.0">
  <require>com.nuxeo.ecm.arender.low.resolution</require>

  <extension target="org.nuxeo.runtime.ConfigurationService" point="configuration">
    <property name="nuxeo.arender.low.resolution.chain">Document.ARenderGetBlob</property>
  </extension>

</component>