Add Prometheus Remote Write Exporter (2/6)

[AzfaarQureshi]

Description

This is PR 2/6 of adding a Prometheus Remote Write Exporter in Python SDK and address Issue open-telemetry/opentelemetry-python#1302

Part 1/6

• Adds class skeleton
• Adds all function signatures

👉 Part 2/6

• Adds validation of exporter constructor commands
• Add unit tests for validation

Part 3/6

• Adds conversion methods from OTel metric types to Prometheus TimeSeries
• Add unit tests for conversion

Part 4/6

• Adds methods to export metrics to Remote Write endpoint
• Add unit tests for exporting

Part 5/6

• Add integration tests using sample app and instance of Cortex

Part 6/6

• Add README, Design Doc and other necessary documentation.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Added class TestValidation in test_prometheus_remote_write_exporter.py

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated
  cc- @shovnik, @alolita

[ocelotl]

Minor changes requested, not enough to not approve this PR 👍

[codeboten]

👍