Add support for inputs specifying task metadata

[erwinvaneyk]

This PR adds support for users to specify headers (and queries)
The main advantage of using headers is that those explicitly do not get recorded anywhere. They are specific to a task and do not get propagated through

It currently uses a quick experimental format detecting inputs with a key header_* as headers and query_* as query params. In the future it might be an option to change it to an object-based format:

headers:
  key: val

Or support both ways of defining headers.

As flybys:

• User can force the Content type of the request
• Updated / improved the documentation of the examples
• Added a util function to limit the printing of a TypedValue to avoid cluttering of the UI.