Removed swagger as direct depency

Removed direct depency to swagger, now only depends standard framework. This version is easy to use with https://github.com/domaindrivendev/Swashbuckle.AspNetCore version 5.x >.

Breaking changes:

• ApplyApiKeySecurityToDocument removed, replaced with ApiKey type that can be used with swagger generator methods. It uses OpenApi types which come from Microsoft framework. See further examples from README.md