Create jump user for metadata science access to testbetrieb

This adds a new jump-metadata users for the testbetrieb jump host which is allowed to:

• connect to metadaten on port 8080, i.e. access internal pages like /metrics/terms via HTTP.
• connect to status on port 5000, i.e. read-only access all logs via journal-web-ui using HTTP.
• connect to status on port 9090, i.e. read-only access to Prometheus including the internal dashboards like /consoles/metadaten_harvester.html.

This should be accompanied by an updated local SSH config at ~/.ssh/config like

Host jump-metadaten
  HostName gl.tb.umwelt.info
  User jump-metadaten
  LocalForward 5000 status:5000
  LocalForward 9090 status:9090
  LocalForward 8080 metadaten:8080

which means that while

> ssh -N jump-metadaten

is running in a terminal, one can access http://localhost:8080/metrics/terms or http://localhost:9090/consoles/metadaten_harvester.html.