[IMP] document: indexation of MS documents

Commit 3ced0ff6 removed the support of Microsoft documents for
indexation. It makes sense for the old formats such as '.doc' since it
requires an external tool ('antiword'), which could lead to a security
issue. However, the new formats such '.docx' are simple xml files,
therefore they could be indexed with the usual XML parsing tools.

opw-677235