[REQUEST]: Document new functionality for APM alerts & rules

[kpatticha]

Description

In 8.8 we added 2 new filters and added a new functionality to group alerts based on specific dimensions that would like to document

Filters

Latency and failed error rate threshold rule

• transaction.name

Error count

• error.grouping_key 

Grouping by

Resources

Filters

issue:

• [APM] Alerts for specific transaction groups and error groups kibana#152329

PRs:

• [APM] Add transaction name filter in latency threshold rule  kibana#154241
• [APM] Add transaction name filter in latency threshold rule  kibana#154241
• [APM] Add transaction name filter in failed transaction rate rule type kibana#155405

Group by

issue:

• [APM] Additional Dimensions to break down alerts kibana#143107

PRs

• Add group-by feature in APM rules kibana#155001

existing how-to guide: https://www.elastic.co/guide/en/kibana/current/apm-alerts.html#apm-create-transaction-alert

Collaboration

The documentation team will investigate the issue and create the initial content.

Point of contact.

Main contact: @kpatticha

Stakeholders:
@sqren
@gbamparop
@benakansara