Improve layout of `viewcal` command

#discussion

Improve the consistency of the viewcal command output for better scanability.

Currently each day is displayed in a table that may have different sizes depending on the times of the events and the event names.

Mockup screenshot

Acceptance criteria

• Define how the viewcal command should render the events
• Document findings in a new issue to handle the task.

Related tasks

• https://github.com/mattermost/mattermost-plugin-mscalendar/issues/315