[FEATURE IDEA] postProcess option

[lal12]

There are cases where the resulting BOM might be wanted to change.
Currently I want to add fields to metadata.compononent (beyond rootComponentType, rootComponentName, rootComponentVersion), add its git repo, add more external components and add to metadata.tools.

My webpack build is currently pulling code from three repos, two libraries and the other one is a collection of templates which are converted to code and imports are automatically generated for them. So I want to track their existence and version of the individual parts of the project.

PR in #672.