Add hook for post-processing of assets after/during upload

The goal is to implement a hook for customers to implement post-processing of assets (PDF’s, Word and Excel files, and others). The use case is desired removal of metadata of from PDFs and other assets. 
 
The reason behind this feature request is that customers want to prevent publishing personal (privacy-sensitive) information on their websites. Currently, this is potentially happening as the metadata of assets contains information such as ‘creator’ of ‘last modified by’ information. The solution for this issue should allow customers to remove all metadata during/after upload. 
 
File types: PDF’s, Word and Excel definitely, but ideally we implement this for all file types.