Updates text of generate-webhook-url-basic.md to replace the use of
the "Create the channel" step.
Removes {!create-channel.md!} from all the integrations docs that
also include {!generate-webhook-url-basic.md!}.
Fixes#32269.
markdown-include is GPL licensed.
Also, rewrite it as a block processor, so that it works correctly
inside indented blocks.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Note that the "Save" button has no text in the Taiga webhook
setup UI. There is a small floppy disk symbol for saving which
is visible right beside the form fields. So I simply said,
"Save the form".
