[APM] Ability to use filtering and breakdowns in APM rules

[sorenlouv]

Problem

We know from the requested alerting rule types that end users want to be able to create alerts for a specific subset of documents (eg. a specific transaction groups), as well as ability to group by a dimension (eg. error group) and alert when a single group exceeds a given threshold. Neither of these two controls are available today so the user can only create rules that monitors the entirety of a service. This means that even if a single transaction group significantly exceeds a given threshold, no alerts will be created as long as the overall service doesn't exceed the threshold. This is problematic because this way important events go unnoticed.

Solution

APM rules should have controls for filtering and breakdowns.

Filtering
Scenario: A user wants to create a rule that monitors the "/checkout" transaction, so they are made aware as soon as the failure rate increases over 1%.
They should be able to do this by using the transactions failure rate rule type, and adding a filter for transaction.name: "/checkout"

Breakdown
Scenario: A user wants to be notified when any of their transaction groups exceed 5000ms latency.
They should be able to do this by using the transactions latency rule type, and then specifying transaction.name.

[elasticmachine]

Pinging @elastic/apm-ui (Team:APM)

[sorenlouv]

Group by was added in #155001. Improved filtering was also added in 8.8 and more is planned in https://github.com/elastic/apm-dev/issues/929