I found how to automate the build and archive process from the comand line, I just wrote a blog article explaining how you can achieve that.
The command you have to use is xcrun
:
/usr/bin/xcrun -sdk iphoneos PackageApplication \
-v "${RELEASE_BUILDDIR}/${APPLICATION_NAME}.app" \
-o "${BUILD_HISTORY_DIR}/${APPLICATION_NAME}.ipa" \
--sign "${DEVELOPER_NAME}" \
--embed "${PROVISONING_PROFILE}"
You will find all the details in the article. If you have any questions dont hesitate to ask.