Adding support for posting data to custom webhook URL

[Sandeep Singh]

Suggested by Roni (on discord)

Example config:-

custom:
  - id: webhook
    custom_webook_url: http://0.0.0.0/api/webhook
    custom_method: GET
    custom_format: '{{data}}'
    custom_headers:
      Content-Type: application/json
      X-Api-Key: XXXXX

[Regala]

This would allow us to also format data? i.e. I'm interested in preserving the colored output from terminal -> to Slack but not sure how/where to do that.

[Sandeep Singh]

@Regala do you example of slack supporting colored output in markdown or any format?

[Regala]

Ugh actually for now seems like only markdown is supported