Feature RQ: Add custom observation options/tags

It would be nice to be able to customize the behavior of the satnogs-client during an observation for specific observations. This could be implemented by custom tags, entered by the user via network when creating an observation and passed to the client.

Possible tags:

• activate IQ data storage & upload
• activate audio upload (in case we disable audio upload for some decoders by default in the future)
• Choose a development-version of a gnuradio flowgraph (Fixes #378)
• overwrite gr-satnogs script arguments, e.g.
  • frequency
  • ppm correction

All the ideas above are related to the debugging of a station or developing satnogs-client/gr-satnogs. The tags would be handed over to the client in a format transparent to satnogs-network, (as in: satnogs-network doesn't know the meaning of the tags), and the client modifies its config accordingly during the observation (non-persistent).

This feature request was extracted from a misplaced comment in #474.