add json /cfg API to documentation

[FlohGro-dev]

I would like to change the preset that should be applied at boot via the json/HTTP API.

Background: I use WLED for a lamp with interchangeable covers (e.g. a lion and a car) - I have different presets for the covers and I don't want to manually reconfigure the applied preset at boot every time I change the cover.

[dosipod]

@FlohGro-dev You can use the end point http://wled-ip/json/cfg

[FlohGro-dev]

Interesting! I couldn't find this in the docs either it's not there or I used the wrong search terms. Will try and close the issue if it's working 😊 thank you @dosipod

[dosipod]

@FlohGro-dev Yes it is not in the docs because no one bothered to updated it , once you tested it ( it will work ) then you might want to consider making a PR for the docs here https://github.com/Aircoookie/WLED-Docs .

The http://wled-ip/json/cfg can work with all configuration based items and if you find any that does not work then report it