Support Json-serialized query parameters in Spring client RestClient and WebClient

[Mattias-Sehlstedt]

Adds support for Json-serialized query parameters.

A query parameter with an array/object/array of objects is most often serialized based upon the explode and style settings. Another less common way of formatting query parameters is by stating that they should be Json-serialized.

Since the RestClient and WebClient were already using an ObjectMapper, I configured so that that is used to serialize any query parameter. This should also mean that it should be easy for a client to adjust a parameter's serialization if the case is that the server does not want the "standard" serialization format that one would expect for an object (i.e., you can inject a custom Json-serialization for any query-object you might have).

I have tested the basic case of a single object and an array of objects in a local project by mirroring the mustache-file changes that I have committed here.

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