Define community engagement goals

**Describe the problem/challenge you have**
See #182 for the overlying _why_.

**Describe the solution you'd like**
We should align on a minimal set of metrics for determining our community engagement success.

**Anything else you would like to add:**
A couple of notes:
- We could consider thinking about this in the [SLI/SLO methology](https://www.atlassian.com/incident-management/kpis/sla-vs-slo-vs-sli). I would recommend keeping the team of maintainers as the primary audience so I would not consider an SLA at this time. Example:
- 90% of initial response times for new issues on GitHub are two business days or less.
- Consider Slack interrupts and GitHub Issues/PRs. Some examples:
- Time to initial response in Slack questions on #carvel and #project-carvel.
- Time to initial response for new Issues on GitHub.
- Time to close Issues on GitHub.
- Time to initial response for new PRs on GitHub.
- Time to close PRs on GitHub.
- This story is only about determining the metrics and the intended success measurement. This story does not include implementing the metrics.

Start by reading #182 and the linked SLI/SLO guidance, then review the listed Slack and GitHub response and closure examples. Done means agreeing on a minimal set of community engagement metrics and intended success measurements; metric implementation is explicitly out of scope.

Written by the indexing model from the issue text.