Add custom headers to the request url for slackbot responses (opens door for use with github actions)

[jasongornall]

Is your feature request related to a problem? Please describe. Github actions require an auth header to be accessed from the web. This opens a massive door for slack to be utilized directly with github actions!!

Describe the solution you'd like optional custom headers to be sent with the request allow for a workflow github action to be utilized with slack responses

Describe alternatives you've considered A firebase function, lambda function, and running my own server via bolt all work too

Additional context I think this would make adding custom slackbots way easier

[ashokirla]

@jasongornall Can you please share a bit more about the use case and how can we help.