[Feature] API documentation for deployed functions

[alexellis]

Feature: API documentation for deployed functions

Several users have asked for the ability to document how to interact with functions which have been deployed on OpenFaaS. This issue is also tracked on the Trello roadmap, see #contributors on Slack.

Expected Behaviour

As a user of functions deployed to OpenFaaS, I want to know how to interact with them, programatically. This should cover input/output format, schema and content-type (mime).

Current Behaviour

BT and other users have implemented custom /docs endpoints within their functions.

[itsmurugappan]

@alexellis This is a utility I developed to document the deployed functions in open api spec 3.0 and visualize it in a swagger ui.
https://github.com/Optum/faas-swagger
Please let me know your thoughts.