IP Geotagging

Add the ability to add fields or tags to data for its geo location based on IP.

Something like:

```
// tag example
|geoIP()
.cityTag('city')
.stateTag('state')
.zipTag('zip')
.countryTag('country')

// or fields
|geoIP()
.cityField('city')
.stateField('state')
.zipField('zip')
.countryField('country')
```

Start by locating the existing geoIP-related operator or field/tag APIs in the Kapacitor codebase and review how operators enrich time-series data. Define the supported IP geolocation fields and tags represented by the issue's examples, then add coverage showing that city, state, ZIP, and country values are produced as requested.

Written by the indexing model from the issue text.