Update MetricStream defaults

[kaylareopelle]

Update the MetricStream class to more closely match the specification: https://opentelemetry.io/docs/specs/otel/metrics/sdk/#stream-configuration

Originally from: https://github.com/open-telemetry/opentelemetry-ruby/pull/1604#discussion_r1683588187

[xuan-cao-swi]

Hi @kaylareopelle,

While I was trying to resolve this spec issue, I came up with more questions.

Based on the spec, all the configuration options are optional (e.g., Users can provide a <>, but it is up to their discretion.). So, I was wondering if we should change the MetricStream class initialization to use dictionary-type parameters?

def initialize(
  name: name,
  description: description,
  unit: unit,
  instrument_kind: instrument_kind,
  meter_provider: meter_provider,
  instrumentation_scope: instrumentation_scope,
  aggregation: aggregation,
  ...
)

FYI, I think MetricStream is not supposed to be accessed or used by end-users because, currently, MetricStream is only used during the initialization of synchronous_instrument. I guess we don’t need to worry about adding new options (e.g., exemplar_reservoir) that might confuse end-users.

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