Function used to send a notification to Slack.

The function receives a map including a text used to build the message, and an options Mmp that can include this configuration:

• url: URL of Slack integration to call.
• username: Username of the bot used to send the notification.
• icon_emoji: Icon to show as the bot avatar (with Slack format, like :bird:)
• channel: Channel or username to send the notification.

It will respond with a tuple, indicating if everything was :ok or there was an :error.