update to demessaging 0.3.0
this updates the backend module to the latest version of 0.3.0. To run this backend module together with the fee-river-plume-workflow frontend, you need to have the version that is compatible with dasf-web
0.3.4 (see digital-earth/flood-event-explorer/fee-river-plume-workflow!4 (merged))
@viktoria-wichert please test this locally before I deploy it on https://hcdc.hereon.de/datahub