Add Support for File types in Open API Connector

[neel015]

Hello SK team!

We have been using the package Microsoft.SemanticKernel.Plugins.OpenApi , it works well with API requests accepting JSON.
However, we have an API which accepts file, for that it is not working.
While taking a look at the repo we can see that only application/json and text/plain are supported.

It would be nice to support file types in API requests.

[evchaki]

@neel015 - we will make this an issue to make sure we get this in for you.