[FR] Openweathermap plugin for Telegraf - addition of 'wind_gust' metric

### Use Case

Greetings,

Openweathermap plugin currently pulls two wind metrics - `wind_speed` and `wind_direction`, but the upstream API also offers the `wind_gust` value.

Sample output from curling the openweather api:

```
 "wind": {
   "speed": 6.43,
   "deg": 155,
   "gust": 16.41
 },
```

Adding this to the telegraf openweathermap plugin _looks_ to require small additions in three places in https://github.com/influxdata/telegraf/blob/master/plugins/inputs/openweathermap/openweathermap.go - a single line entry after each of the three existing
```
"wind_degrees": e.Wind.Deg,
"wind_speed": e.Wind.Speed,
```
definitions, with `wind_gust` as the API returned key name, and `e.Wind.Gust` as the new internal variable.

And one line addition to: https://github.com/influxdata/telegraf/blob/master/plugins/inputs/openweathermap/types.go - adding a new entry after:
```
Wind struct {
Deg float64 `json:"deg"`
Speed float64 `json:"speed"`
```
I'd assume same type (float64 and speed) as 'Wind.Speed'.

I'd guess some adds to the output samples and the /testcases/ directory, but I'm not a go lang guy, so I'm going to avoid guessing about those requirements.

thanks,
Jedd.

### Expected behavior

n/a

### Actual behavior

n/a

### Additional info

_No response_

Start in plugins/inputs/openweathermap/openweathermap.go and types.go, following the existing wind_degrees and wind_speed mappings and Wind struct fields. Check the output samples and testcases directory for related expectations. Done means the upstream gust value is represented as wind_gust and covered consistently in the samples or tests.

Written by the indexing model from the issue text.