chore: cloudwatch metrics example

[anitarua]

Addresses #442. Created a new lambda-examples directory to show how a CDK stack can be configured to deploy a Lambda function or ECS cluster, create metric filters for the associated log groups (or a custom log group), and create a CloudWatch dashboard.

The dashboard looks something like this when populated (updated dashboard):

The dashboard uses values in the logs emitted by both the Nodejs SDK metrics and .NET SDK metrics interfaces.

Also tested that this works with a .NET lambda function (that work currently exists in an unmerged branch but can merge into the dotnet repo if it seems useful).

Let me know if you think the dashboard should include/exclude any other metrics!

Original dashboard when PR opened:

[cprice404]

this is looking awesome!

i want to test it in my account before we merge it, and not sure if i will get to that today. but i left a handful of minor feedback that I think you could go ahead and move forward on when you have bandwidth.

[cprice404]

anita i deployed this locally and started playing with it, but ran out of time. I will finish reviewing this evening!

[cprice404]

this is looking really awesome. I left some comments for us to fine tune the dashboard widgets in this last mile, to make them more realistic for an operator dashboard, but this is really great and I can see the finish line!

[anitarua]

Lots of great feedback, thanks!! Here's what the dashboard looks like now

[cprice404]