Update config/metrics/counts_28d/20210216180622_incident_management_total_unique_counts_monthly.yml

What does this MR do and why?

Adding the following events to the incident_management_total_unique_counts aggregate metrics:

 - incident_management_resource_links_created
 - incident_management_resource_links_edited
 - incident_management_resource_links_deleted
 - incident_management_alert_create_incident
 - quickactions_promote_to_incident
 - quickactions_publish
 - quickactions_severity

Updates to weekly active users were done in a separate MR, Updating Respond Group GMAU (!98245 - closed).

Describe in detail what your merge request does and why.

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MR acceptance checklist

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