Post a test message to the slack channel

curl --request POST \
  --url https://{hostname}.gable.ai/v0/slack/test \
  --header 'Content-Type: application/json' \
  --header 'X-API-KEY: <api-key>' \
  --data '
{
  "channelId": "<string>"
}
'

{
  "message": "<string>"
}