Support alternative swagger.json file

[chazsconi]

We need to support the K8S metrics-server API (https://github.com/kubernetes-incubator/metrics-server) in our implementation.

To do this I need to fork the Kazan repo to make the following changes:

• Use a different swagger.json which included the metrics-server endpoints
• Add two lines to Kazan.Codegen.Naming to map the metrics namespace

(https://github.com/chazsconi/kazan/commit/cd923bcab39a0a593b628ddb7d06fc87d694c6e9#diff-1856cab08f35cbaee3b304822e1699c4)

It would be nice if these two things could be set via the configuration.

Additionally I also had to manually change the swagger.json so the window field is a string rather than a Duration cause a crash when decoding, but this is really a different issue, and I'm not sure how to fix it properly.

https://github.com/chazsconi/kazan/commit/0e44c4ec6ca5f691443bad766f83c9147f9d2812

[obmarg]

Hey @chazsconi. This sounds like a useful feature to have, and I could probably throw it together pretty easily. How does swagger.json work when you've got something like metrics-server installed? Does k8s give you an updated swagger.json with all it's endpoints and any extra stuff you've got installed, or did you have to glue together something youreself?

[chazsconi]

@obmarg When you have metrics server installed, the endpoint /swagger.json will give you the updated file - no need to glue it together manually.

[obmarg]

@chazsconi I've put together a PR with this functionality in #57 if you want to take a look/try it out.

[chazsconi]

@obmarg Works well - thanks a lot! I added a comment in the PR.