Extend /surveys endpoint to include waterlevel_value * Change SQL to use the same strategy as used in schema/gemma.sql for bottlenecks_geoserver to determine the waterlevel_value. * Extend go controler to deal with the situation where the value is not there. This is still suboptimal as this creates a json object for the NullInt64 value.

`dot.tmpl` is a template file for `postgresql_autodoc`
to be more similiar to UML and leave out some less useful labels.

See  `../docker/README.md`