Support publication of snow data in wis2box

[maaikelimper]

surface-based-observations/snow

! verify topic

• [ ] Discovery metadata
• [ ] Sample data files
• [ ] Station list updated
• [ ] Tests updated

[maaikelimper]

• snow data should be on GTS or from ECMWF (@efucile to consult w/ Rodica)
• Synoptic snow data can provide an example