Prefix types with `global::` so that we don't get conflicts with property names

[jakejscott]

We are getting namespace error's because the models are not prefixed with global::

Here's an example of the problem

And here's how it could be fixed by prefixing models with global:: like people do with source generators.

[jakejscott]

I think this has been fixed in kiota 1.16.0 https://github.com/microsoft/kiota/releases/tag/v1.16.0