[native] Add support for Sentry Metrics

[smeubank]

Description

Metrics! Sentry will support Metrics finally! First we need all of our SDKs to support Metrics, including the Native SDK

*this will also enable that our Unreal Game Engine SDK could support Metrics

Requirements:

• API for sending Metrics, add protocol definitions for sending statsd envelope items
• Metrics Summary
• Code location, linking metrics to source code
• Tag normalization

Document(s)

Develop Specs
SDK Develop Specs
Product Specs