Review API Gateway configuration docs

[achmelo]

Is your feature request related to a problem? Please describe. It seems that API gateway configuration docs contain information that should be included in different sections. It would be good to review it. An example of an incorrect location is https://docs.zowe.org/stable/user-guide/api-mediation/api-gateway-configuration#change-password-with-saf-provider it should be in something like Gateway service REST API doc