openapi all in one json

**Is your feature request related to a problem? Please describe.**

When I generate several clients from swagger APIs, I get duplicate definition of Match and Ticket, and other types. I have manually map these and write extensions/methods.

**Describe the solution you'd like**

I seems can generate protobuf types which all share same types, so may be it is possible either to link one swagger json in other or merge all jsons from https://github.com/googleforgames/open-match/tree/main/api into one big swagger.

**Describe alternatives you've considered**

I do not use GRPC anywhere in the project. Agones API is also HTTP.

**Additional context**
I am on C# and use NSwag

Start by inspecting the OpenAPI files in the api directory and the current NSwag client-generation workflow described in the issue. Determine whether the APIs can be linked or merged while sharing definitions, then verify that the resulting single JSON generates C# clients without duplicate Match, Ticket, or other types.

Written by the indexing model from the issue text.