add url params to fetch

[kotontrion]

this PR adds a params to the options of fetch. These two are equivalent:

Utils.fetch('https://wttr.in/?format=3')
const options = {
  params: { format: 3 }
}
Utils.fetch('https://wttr.in/', options)

This is especially useful, if the params are created dynamically, as the users won't have to handle encoding themself.
This is not part of the web fetch api, but i think this is still useful, as unlike the web, there is no URLSearchParamsin gjs.
I did some testing on this and this is compliant with the url scheme.

[kotontrion]

the param will be parsed as follows:
primitive types => key=value
arrays => key=value1&key=value2
objects => key=[JSON representation of object]

the way arrays is parsed is commonly accepted, but there is no standardized way to pass objects, so i just pass the object as json, otherwise it would be passed as [Object object], which is definitely wrong.