Fix web_url output; add json output

[wdconinc]

The webhook returns a json object with the web_url of the created pipeline. This fixes how this link is passed to the calling workflow (and provides access to the full json object).

Other small changes:

• webhook call is not printed (not scalable and not useful beyond debugging),
• use checkout to get current repository for testing, not a released version upstream.

[wdconinc]

"Secrets are not passed to workflows that are triggered by a pull request from a fork."

Apparently neither the secrets in this repository nor those in the fork are used. So, pull requests from forks will just always have failing workflows...