Datastream Extract: define custom extract file name

Per default the name of each extract is {datastreamtype}-{datastream-id}-{uuid}
e.g.: adwords-230-20171208-dbd25e9a223b48ac87649965a81966af.csv
For File Server/S3 destinations or when processing Excel/CSV files it can be necessary to name data extracts different to this default.
Use the command set_meta with fieldname datastream_extract_filename to change the extract's name.
You can either use a dynamic value based on another column (option 1) or a static value (option 2) as visualized in the two examples below: