Fix Azure Monitor support for multiple aggregation types

[zmoog]

Proposed commit message

Fixes two bugs related to supporting multiple aggregation types.

1. Use aggregation type in MetricRegistry in the cache key.
2. Create one KeyValuePoint for each aggregation type

(1) Use aggregation type in MetricRegistry in the cache key

The MetricRegistry.NeedsUpdate checks if a metric definition needs an update. If there are multiple metrics config with no dimensions:

  resources:
  - metrics:
    - aggregations:
        - Maximum
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces
    - aggregations:
        - Minimum
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces
    - aggregations:
        - Average
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces

All three metric configs end up having the same key, ending up skipping the metric collection for the second and third configs.

By adding the aggregation type in the cache key, we can correctly keep track of metric updates.

(2) Create one KeyValuePoint for each aggregation type

Add support for multiple aggregation types in the mapToKeyValuePoints() function to restore support for configs like the following:

  resources:
  - metrics:
      namespace: Microsoft.EventHub/Namespaces
      aggregations:
        - Average
        - Maximum
        - Minimum
      ignore_unsupported: true
      timegrain: PT1M

I missed this feature in a previous change. Unfortunately, no existing modules or integrations use multiple aggregation types, and no tests exist.

We are adding more tests targeting to cover all existing use cases soon.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] ~~I have made corresponding changes to the documentation~~
• [ ] ~~I have made corresponding change to the default configuration files~~
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• [ ] Cover all multiple aggregation type use cases with tests

How to test this PR locally

Related issues

• Closes https://github.com/elastic/beats/issues/39192

Use cases

The PR must support multiple aggregation types in two different variants:

• multiple aggregation types in one metric group
• one aggregation type in multiple groups with the same metric

Here are two variants of the metric ActiveConnections with three aggregation types: Maximum, Minimum, and Avergate:

- module: azure
  metricsets:
    - monitor
  enabled: true
  period: 60s
  client_id: '<redacted>'
  client_secret: '<redacted>'
  tenant_id: '<redacted>'
  subscription_id: '<redacted>'
  refresh_list_interval: 600s
  resources:
  - metrics:
    - aggregations:
        - Maximum
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces
    - aggregations:
        - Minimum
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces
    - aggregations:
        - Average
      ignore_unsupported: true
      name:
        - ActiveConnections
      namespace: Microsoft.EventHub/Namespaces

This variant should be preferred since in needs less API calls to fetch the same data:

- module: azure
  metricsets:
    - monitor
  enabled: true
  period: 60s
  client_id: '<redacted>'
  client_secret: '<redacted>'
  tenant_id: '<redacted>'
  subscription_id: '<redacted>'
  refresh_list_interval: 600s
  resources:
  - metrics:
      namespace: Microsoft.EventHub/Namespaces
      aggregations:
        - Average
        - Maximum
        - Minimum
      ignore_unsupported: true
      timegrain: PT1M

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[gizas]

LGTM and the tests run successfully on myside