Add MSG to EML email conversion support (#367)

- Add new msgconvert converter using libemail-outlook-message-perl
- Support conversion from Outlook MSG files to standard EML format
- Add msgconvert to Docker dependencies and version checking
- Register msgconvert converter in main converter registry

Implements feature request #367 for email format conversion

Dockerfile

@@ -59,6 +59,7 @@ RUN apt-get update && apt-get install -y \
   libreoffice \
   libva2 \
   libvips-tools \
+  libemail-outlook-message-perl \
   lmodern \
   mupdf-tools \
   pandoc \