Serve OpenAPI v2 (swagger) and v3 HTTP docs

[tdeebswihart]

What changed?

v2 docs are served at /api/v1/swagger.json while v3 is at /api/v1/openapi.yaml

Why?

So that users know what we expect for our various HTTP APIs

How did you test it?

Check out https://github.com/temporalio/api-go/pull/146 at ../api-go

$ curl localhost:7243/api/v1/swagger.json
$ curl localhost:7243/api/v1/openapi.yaml

Potential risks

None

Is hotfix candidate?

No