[Tagging] Self serve and full serve gas stations

[Andrew MacKinnon]

I would like to propose that the tag full_service=yes be used to tag
gas stations that are full serve (i.e. an attendant pumps gas, like
all gas stations in New Jersey and Oregon).

The tag self_service=yes is already used for gas stations, but some
gas stations are both self serve and full serve and charge a higher
price for full serve. Thus I think that self_service=no should not be
used in the context of gas stations.