Added logout command

[Prashant-7718]

MermaidChart Logout is added to command pallet for users to get logged out from mermaid account

1. To test locally:

• Take a pull with this branch
• Open in Vsocde code and run the plugin
• This will open new window and will prompt for authentication
• Authenticate with correct user
• use this document for authenticating user (https://mermaidchart.atlassian.net/wiki/spaces/Plugins/pages/457441288/Cursor+Vscode+plugin+testing)
• Open Command Palette
• Select Command: Search for and select the MermaidChart Logout command.
• Execute Logout: Confirm the logout action.
• Verify Logout: Ensure you are logged out and A logout confirmation popup should be displayed.

2. To test After release:

• Install Mermaid Chart Plugin
• Log In: Start by logging into the plugin
• Open Command Palette
• Select Command: Search for and select the MermaidChart Logout command.
• Execute Logout: Confirm the logout action.
• Verify Logout: Ensure you are logged out and A logout confirmation popup should be displayed.