Add kotlinx serialization extension methods for HttpFetcher

[bitspittle]

See also: https://github.com/varabyte/kobweb/discussions/599

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Essentially, add methods for all HTTP verbs (e.g. window.http.get<MyType>(...)) to this module: https://github.com/varabyte/kobweb/tree/main/common/kobwebx-serialization-kotlinx/ (or maybe make a sibling module if that ends up being an inappropriate place to put stuff)

[bitspittle]

(Set to 1.1 so this won't get lost in the noise in the future. Not against this going into 1.0 by any means though.)