…demy badge

📝 (enable-copilot.rst): Include Mattermost Academy badge and update API URL instructions
The new file academy-copilot-setup.rst was added to include a Mattermost Academy badge that links to a tutorial on setting up and configuring Mattermost Copilot with multiple LLMs. This badge was then included in enable-copilot.rst to provide users with a direct link to the tutorial. The instructions for entering the API URL were also updated to clarify the URL format for services other than Ollama.