Allow users to select environmental variables of interest from NASA POWER

[issy-ukceh]

https://github.com/AMI-system/EntoInsights/blob/ef2900c697990797db1ff67fda74ef570fbd83cc/R/get_hourly_env_data.R#L153C3-L153C93

Currently the get_hourly_env_data function automatically gets data for 8 different environmental variables. It would be nice to give an option to select only the variables you're interested in to avoid requesting unnecessary data, which can be quite slow.

[issy-ukceh]

Around 3.5 mins to run get_hourly_env_data for 36 locations across 15 weeks