services/alert-metrics: add avgTimeToAck and avgTimeToClose chart

[KatieMSB]

• Identified the issue which this PR solves.
• Read the CONTRIBUTING document.
• Code builds clean without any errors or warnings.
• Added appropriate tests for any new functionality.
• All new and existing tests passed.
• Added comments in the code, where necessary.
• Ran make check to catch common errors. Fixed any that came up.

Description:
This pr adds new alert metrics chart for visualizing time to acknowledge and time to close averages for daily alerts.

Which issue(s) this PR fixes:
Closes #2313

Screenshots:
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Describe any introduced API changes:

# adds new metrics to AlertDataPoint type
type AlertDataPoint {
  timestamp: ISOTimestamp!
  alertCount: Int!
  avgTimeToAck: ISODuration # only null if alertCount is 0
  avgTimeToClose: ISODuration # only null if alertCount is 0
}

[mastercactapus]

approving just to test in CI; time/space code will be moved to it's own PR before merging

[tony-tvu]

lgtm!