[ECR] [feature request]: ECR Console Dashboard

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**Tell us about your request**
Add a dashboard to the ECR Console, akin to the dashboards available for other services, e.g. inspector and rds. The ECR dashboard would provide aggregate/summarised information and metrics about the registry, such as the total number of repositories, total number of images across all repos and by repo, perhaps image counts grouped by age (histogram), total image pulls from the registry and by repo and by image, show the top10 of image pulls, image push distribution, etc...

**Which service(s) is this request for?**
ECR

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Such a dashboard would be useful for us (and others) that have 100s or 1000s repos and .10k images on ECR. Today, we have to pull a lot of metadata off ECR and CloudTrail to "manually" assemble such dashboards... painful :-)

**Are you currently working around this issue?**
yes, painfully so :-)... we have to pull a lot of metadata off ECR and CloudTrail to "manually" assemble such dashboards.

The issue names no repository files, tests, or implementation entry points. Start by reviewing how ECR and CloudTrail expose repository, image, pull, and push metrics, then establish an agreed dashboard scope. Done means the selected aggregate metrics and their presentation are specified and implemented.

Written by the indexing model from the issue text.