Merge the new_sdk/main branch into main

[MrAlias]

Blocked by all issues in https://github.com/open-telemetry/opentelemetry-go/milestone/22. This will be the last issue that closes the milestone.

• Create a PR to merge new_sdk/main into main
  • Update the changelog entries added in Add new metric SDK changes to changelog #3150 with the PR number
• Delete new_sdk/main
• Delete new_sdk/example

[MrAlias]

This needs to include deleting the new_sdk/example branch. It will no longer be needed.

[MrAlias]

The PR number needs to be added to the changelog entries added in #3150

[MrAlias]

Merging will orphan the following packages:

• go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest
• go.opentelemetry.io/otel/sdk/metric/aggregator/histogram
• go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue
• go.opentelemetry.io/otel/sdk/metric/aggregator/sum
• go.opentelemetry.io/otel/sdk/metric/aggregator
• go.opentelemetry.io/otel/sdk/metric/controller/basic
• go.opentelemetry.io/otel/sdk/metric/controller/controllertest
• go.opentelemetry.io/otel/sdk/metric/controller/time
• go.opentelemetry.io/otel/sdk/metric/export/aggregation
• go.opentelemetry.io/otel/sdk/metric/export
• go.opentelemetry.io/otel/sdk/metric/number
• go.opentelemetry.io/otel/sdk/metric/processor/basic
• go.opentelemetry.io/otel/sdk/metric/processor/processortest
• go.opentelemetry.io/otel/sdk/metric/processor/reducer
• go.opentelemetry.io/otel/sdk/metric/registry
• go.opentelemetry.io/otel/sdk/metric/sdkapi
• go.opentelemetry.io/otel/sdk/metric/selector/simple

Do we want to plan a deprecation strategy for these? (Related to #2328)

[jmacd]

Question about go.opentelemetry.io/otel/sdk/metric/aggregator/exponential/mapping (which exists today and should stay somewhere).
I think it's OK if that package moves.

[MrAlias]

Question about go.opentelemetry.io/otel/sdk/metric/aggregator/exponential/mapping (which exists today and should stay somewhere). I think it's OK if that package moves.

Indeed, this needs to be migrated to the new SDK. Please create an issue and add it to the beta milestone so we can track the work.