Support local file as JSON source

[adamhassel]

Is your feature request related to a problem? Please describe.

I'd love to be able to use a local file with JSON as the source. I'm generating the JSON myself anyways, and it seems overkill to have to spin up an http server to get a bunch of bytes sent, that might as well be a file on disk next to the module config, for example. I'll be updating the data in the json file indenpendently.

This would also be a great tool to test the module output without the need for constant request refreshes. There might be people using pay-per-request sources...

Describe the solution you'd like

I know that fetch doesn't support serving local files, but maybe make a new config directive, file or something, with that and url being mutually exclusive? Or have url support file://<path> and detect that in code?

Describe alternatives you've considered

Short of spinning up a webserver, I don't see an obvious alternative....

[DanielHabenicht]

It think I would go for the second alternative of adding a file Configuration option.

I don't have time for a least two weeks, but if you want to take a shot you can make a PR an I will review it.