Restructures the integration documentation pages to use a style
that's more similar to the help center documentation, with an
instruction block for setting up the integration, and sections
for additional configuration information and related documentation
links.
Updates the doc pages for the airbrake, azuredevops and gitlab
integrations as examples of the updated style.
Also updates the URL specification section of the incoming webhook
overview in the API documentation so that the documented URL
parameters can be linked to directly in the integration doc pages.
Co-authored-by: Alya Abbott <alya@zulip.com>
Lauryn Menard