Add sums to internal events

What does this MR do and why?

Adds a rudimentary implementation of sum to Internal events. Motivated by this and this

All features, like all time and time time framed metrics and filtering works.

Sum metrics can be defined like this:

[snip]
events:
  - name: my_event
    operator: sum(value)

This MR does not include docs or CLI support as it is the first iteration we need to implement the first metrics.

In the monitor trigging three events could look like this:

(sums.sum_total_my_events_with_foo is filtering label: foo and sums.sums_total_my_event_monthly is summing all events)

References

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Before	After

How to set up and validate locally

Create the following files:

ee/config/events/my_event.yml

---
description: Test sum metrics
internal_events: true
action: my_event
additional_properties:
  label:
    description: Something to filter by
  value:
    description: Number of something
product_group: analytics_instrumentation
milestone: '17.6'
introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170920
distributions:
- ee
tiers:
- ultimate

ee/config/metrics/counts_28d/count_total_my_event_monthly.yml

---
key_path: sums.sum_total_my_event_monthly
description: Monthly sum of value from my_events
product_group: analytics_instrumentation
performance_indicator_type: []
value_type: number
status: active
milestone: '17.6'
introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170920
time_frame: 28d
data_source: internal_events
data_category: optional
distribution:
- ee
tier:
- ultimate
tiers:
- ultimate
events:
- name: my_event
  operator: 'sum(value)'

ee/config/metrics/counts_all/count_total_sum_total_my_events_with_foo.yml

---
key_path: sums.sum_total_my_events_with_foo
description: Sum count of my_events with foo
product_group: analytics_instrumentation
performance_indicator_type: []
value_type: number
status: active
milestone: '17.6'
introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170920
time_frame: all
data_source: internal_events
data_category: optional
distribution:
- ee
tier:
- ultimate
tiers:
- ultimate
events:
- name: my_event
  operator: 'sum(value)'
  filter:
    label: foo

To verify:

1. Run the monitor bin/rails runner scripts/internal_events/monitor.rb my_event
2. Trigger some events:

   Gitlab::InternalEvents.track_event('my_event', additional_properties: {label: 'bar', value: 1.1})
   Gitlab::InternalEvents.track_event('my_event', additional_properties: {label: 'foo', value: 2.4})
   Gitlab::InternalEvents.track_event('my_event', additional_properties: {label: 'foo', value: 0.6})

3. Check the monitor