Update njs/nswag packages for better external ref handling (#17)
* Update NJS. NSwag, Namtion, YamlDotNet packages
* ToString overrides for results
* Update integration tests with better asserts
* New OpenApiHeader type
* Add Content-Language header
* Another body validation integration test
* Remove specs folder to set up submodule, update ci.yaml
* Update copy settings
* Short-circuit integration tests for external use
* Short circuit E2E tests in the case of missing SpecToken
* Test constant for integration test constant
* Better handling of missing spec tokens in E2E tests
* appsettings.json comment in E2E setup
Also included comments for omitting specToken lines for template use
