fix: `Json` configuration not applying when using custom `HttpClient`

[JellyBrick]

[JellyBrick]

Any updates?

[lukellmann]

i will take a look later

[lukellmann]

We actually don't use the ContentNegotiation plugin, right @DRSchlaubi? The only thing it seems to do for us is adding an Accept: application/json header to our requests, which is probably useless. So we might instead just remove this configuration of the ContentNegotiation plugin.

[DRSchlaubi]

That's correct we don't use it as of now