autocomplete: adjust popularity field weight

[missinglink]

I'm curious as to what effect changing the popularity:weight for autocomplete from 1->2 would have for:

• https://pelias.github.io/compare/#/v1/autocomplete?text=statue+of+liberty
• https://pelias.github.io/compare/#/v1/autocomplete?text=statue+of+liberty+nyc

seems it's been 7 years since we last touched this setting 😱 #338

[missinglink]

A setting of 5 shows some improvement, but I think we might need to go a little deeper and configure two additional values of field_value_factor, the factor and modifier options would allow us to define a better decay curve.

As it currently stands we're finding that the impact of the popularity of a minor monument ~2000 and a major monument ~64000 have a similar effect on scoring, I think we'd want to bend the curve so major monuments have a major impact but minor ones only have a minor impact. The max-boost of 20 seems about right though, as a safeguard.