(cloudwatch): contributor insights widget

I propose to add a construct for a widget to show data from contributor insights rules.
This widget can currently be added using the cloudwatch console, but not easily with the CDK.

### Use Case

I would like to see contributor insights data on my dashboards.

* [x] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

---

This is a :rocket: Feature Request

Start by examining the existing CloudWatch dashboard widget constructs and how contributor insights rules are represented in the CDK. Done means users can add a contributor insights widget to a dashboard through a construct, with coverage for the resulting widget behavior; the issue names no files or tests to begin from.

Written by the indexing model from the issue text.