Revises section to use headers for the possible parameters so that
they can be linked to directly from other documentation pages.
Updates base URL text to read more clearly when rendered.
As the help center article now has detailed instructions to generate
an incoming webhook URL, the integration documentation only needs to
link to that information.
Updates the shared integrations documentation on generating a URL for
an incoming webhook for the new modal in the web-app, with links to the
help center. Also, links to a new section in the incoming webhooks
overview in the API documentation about the URL specification.
Also, adds a link to the help center in the shared webhooks integration
instructions for creating a stream for an incoming webhook. And updates
the example webhook URL to use a stream ID instead of a stream name.