[Feature request] Add OpenAPI definition from file

[artemklevtsov]

Add to add_route method the openapi_file param with OpenAPI definition YAML file.

[dselivanov]

Eventually I ended up with putting openapi to a separate yaml file using it as API definition. I found it is easier to maintain, so at the moment I almost don't use inline annotations inside functions:

app = RestRserve::RestRserveApplication$new()
PATH_TO_OPENAPI_DEFINITIONS_FILE = "openapi.yaml"
SWAGGER_UI_ENDPOINT_PATH = "/swagger"
OPENAPI_ENDPOINT_PATH = "/openapi.yaml"

app$add_static(path = OPENAPI_ENDPOINT_PATH, 
  file_path = PATH_TO_OPENAPI_DEFINITIONS_FILE, 
  content_type = "application/yaml")

app$add_swagger_ui(path = SWAGGER_UI_ENDPOINT_PATH,
                   path_openapi = OPENAPI_ENDPOINT_PATH)
app$run(8080)