Draft: HTTP callbacks as event handler/notification

[dnsmichi]

Shell scripts for event handlers need to be deployed. Most recently, a community member asked how to rewrite a bash script with curl into Python with requests.

Also, we have a couple of tools already around:

• DSL with runtime functions as custom variables
• JSON.encode/decode
• Http Client C++ code in the background
• Access to the runtime state of an object, either through macros or direct object access

The thing I'd like to discuss here:

• An EventCommand which just uses http-callback as executed method
  • Additional variables need to be defined in a specified format, e.g. with creating a DSL function filling the required fields.
• A NotificationCommand which fires http-callback and additional credentials stored somewhere, plus the POST body.
• Execution location configuration - either local or command_endpoint

Similar things are available with GitLab webhooks already.

Describe the solution you'd like

A clear way of configuring this inside the DSL. The user requirement for notifications needs to be lifted.

Also, blocking callbacks shouldn't block other operations, so might need a different task pool here, than the checker component uses.

Describe alternatives you've considered

A Python script which takes care about argument handling and curl requests.