[FEATURE] Display Maintainers last engagement date in a Dashboards visualization

[bshien]

Is your feature request related to a problem?

We need to get a sense of how large the problem is of inactive maintainers, so we should use the maintainer activity data present in the maintainer_engagement index and display a visualization to see how many maintainers are inactive.

What solution would you like?

Display a visualization on metrics.opensearch.com with a mapping between repo, maintainer, affiliation, date last engaged on the repo, and inactivity status.

Do you have any additional context?

Part of #57