[SDK] MetricFilter needs a new AttributeProcessor to handle IncludeExclude

[marcalff]

Metric filtering allows to include or exclude some attributes during metric collection.

The declarative configuration defines attribute_keys filtering with:

• an include list
• an exclude list

See also the SDK spec for stream configuration:

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#stream-configuration

The opentelemetry-cpp SDK needs to provide a proper subclass of AttributeProcessor to implement this behavior.

Current AttributeProcessor subclasses like FilteringAttributesProcessor only implement partially the desired filtering.

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[nikhilbhatia08]

Hey marcalff! I would like to pick up this issue and try it. Thanks!

[marcalff]

@nikhilbhatia08

The relevant part from the spec given in link is:

attribute_keys: This is, at a minimum, an allow-list of attribute keys for measurements captured in the metric stream. The allow-list contains attribute keys that identify the attributes that MUST be kept, and all other attributes MUST be ignored.

Implementations MAY accept additional attribute filtering functionality for this parameter.

Users can provide attribute_keys, but it is up to their discretion. Therefore, the stream configuration parameter needs to be structured to accept attribute_keys, but MUST NOT obligate a user to provide them. If the user does not provide any value, the SDK SHOULD use the Attributes advisory parameter configured on the instrument instead. If the Attributes advisory parameter is absent, all attributes MUST be kept.

Additionally, implementations SHOULD support configuring an exclude-list of attribute keys. The exclude-list contains attribute keys that identify the attributes that MUST be excluded, all other attributes MUST be kept. If an attribute key is both included and excluded, the SDK MAY fail fast in accordance with initialization error handling principles.

This is to be implemented in a sub class of opentelemetry::sdk::metrics::AttributesProcessor.