Spec tracking: Support MetricFilter

[dashpole]

The specification defines a MetricFilter function which filters metrics from a MetricProducer and from the metrics SDK.

MetricFilter is currently experimental, and must not be exposed as part of the public API of the sdk/metric package if implemented. Prior to opening a PR, this issue must have an approved implementation plan, posted as a comment by the assignee, and signed off by a maintainer.

The following links include the specifications related to MetricFilter:

• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricreader
• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#produce-batch
• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricfilter

_{Tip: React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it. Learn more here.}