Spec tracking: MeterConfigurator and MeterConfig

[dashpole]

The specification defines a MeterConfigurator function which computes the MeterConfig for a Meter.

MeterConfigurator is currently experimental, and must not be exposed as part of the public API of the metric or sdk/metric packages 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 MeterConfigurator:

• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#meterconfigurator
• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#meter
• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#meter-creation
• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#meterconfig

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