Migrate Metrics SDK "data' package to Attributes#3352

Merged

jkwatson merged 8 commits intoopen-telemetry:mainfrom jsuereth:wip-labels-to-attributes

Jul 1, 2021

+2,623-1,613

Commits on Jun 24, 2021

Update java metrics data model and create assertion based testing library.
jsuereth
committed

Commits on Jun 26, 2021

Update existing SDK for Label => Attribute in data model
jsuereth
committed

Commits on Jun 27, 2021

Commits on Jun 28, 2021