Task: Mattermost slash command

n8n workflow:
{"nodes":[{"name":"HTTP Request","type":"n8n-nodes-base.httpRequest","position":[650,300],"parameters":{"url":"http://www.lovelyinsults.com/","options":{},"responseFormat":"string"},"typeVersion":1},{"name":"HTML Extract","type":"n8n-nodes-base.htmlExtract","position":[850,300],"parameters":{"options":{},"extractionValues":{"values":[{"key":"Insult","cssSelector":"h2"},{"key":"Permalink","attribute":"data-href","cssSelector":".fb-like","returnValue":"attribute"}]}},"typeVersion":1},{"name":"Webhook","type":"n8n-nodes-base.webhook","position":[450,300],"webhookId":"23be397b-fb1f-4f84-8d41-24fbb2f504a2","parameters":{"path":"23be397b-fb1f-4f84-8d41-24fbb2f504a2","options":{},"httpMethod":"POST"},"typeVersion":1},{"name":"Mattermost","type":"n8n-nodes-base.mattermost","position":[1300,450],"parameters":{"message":"=@{{$node[\"Webhook\"].json[\"body\"][\"user_name\"]}} sent an insult to {{$node[\"Webhook\"].json[\"body\"][\"text\"]}}","channelId":"={{$node[\"Webhook\"].json[\"body\"][\"channel_id\"]}}","attachments":[{"title":"={{$node[\"HTML Extract\"].json[\"Insult\"]}}","title_link":"={{$node[\"HTML Extract\"].json[\"Permalink\"]}}"}],"otherOptions":{}},"credentials":{"mattermostApi":"chat.electronicmun.org"},"typeVersion":1},{"name":"IF","type":"n8n-nodes-base.if","position":[1050,300],"parameters":{"conditions":{"string":[{"value1":"={{$node[\"Webhook\"].json[\"body\"][\"text\"]}}"}]}},"typeVersion":1},{"name":"Mattermost1","type":"n8n-nodes-base.mattermost","position":[1300,200],"parameters":{"message":"=@{{$node[\"Webhook\"].json[\"body\"][\"user_name\"]}} asked me to send an insult, but didn't tell me who to send it to :man_facepalming:","channelId":"={{$node[\"Webhook\"].json[\"body\"][\"channel_id\"]}}","attachments":[{"title":"={{$node[\"HTML Extract\"].json[\"Insult\"]}}","title_link":"={{$node[\"HTML Extract\"].json[\"Permalink\"]}}"}],"otherOptions":{}},"credentials":{"mattermostApi":"chat.electronicmun.org"},"typeVersion":1}],"connections":{"IF":{"main":[[{"node":"Mattermost1","type":"main","index":0}],[{"node":"Mattermost","type":"main","index":0}]]},"Webhook":{"main":[[{"node":"HTTP Request","type":"main","index":0}]]},"HTML Extract":{"main":[[{"node":"IF","type":"main","index":0}]]},"HTTP Request":{"main":[[{"node":"HTML Extract","type":"main","index":0}]]}}}