New layout for Metric Monitor notifications

We've released an updated layout for the notifications from Metric Monitor. In the last 6 months, we’ve dramatically expanded the functionality of this monitor. The layout for its notifications were not coping well with all the new functionality, so it was due for a refresh.

We’ve paid special attention to:

• Simplicity of language
• Consistent use of code format
• Consistency across different recipient types (e.g. not just optimizing for Slack)
• Both mobile and desktop experience