Use environment variables for tracer and meter providers

[ocelotl]

Fixes #1569

Description

Meter and Tracer provider environment variables were not consistent with the rest after Configuration was removed, this fixes that problem.

Fixes #1569

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A

Does This PR Require a Contrib Repo Change?

Answer the following question based on these examples of changes that would require a Contrib Repo Change:

• The OTel specification has changed which prompted this PR to update the method interfaces of opentelemetry-api/ or opentelemetry-sdk/

• The method interfaces of opentelemetry-instrumentation/ have changed

• The method interfaces of test/util have changed

• Scripts in scripts/ that were copied over to the Contrib repo have changed

• Configuration files that were copied over to the Contrib repo have changed (when consistency between repositories is applicable) such as in

  • pyproject.toml
  • isort.cfg
  • .flake8

• When a new .github/CODEOWNER is added

• Major changes to project information, such as in:

  • README.md
  • CONTRIBUTING.md

• 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

[aabmass]

Should we remove the provider arg altogether? I don't see when it would be anything different, its hardcoded in both spots:

opentelemetry-python/opentelemetry-api/src/opentelemetry/metrics/__init__.py

Line 608 in cf8b70e

_METER_PROVIDER = _load_meter_provider("meter_provider")

opentelemetry-python/opentelemetry-api/src/opentelemetry/trace/__init__.py

Line 457 in 18761d7

_TRACER_PROVIDER = _load_trace_provider("tracer_provider")

[lzchen]

Are these defined in the spec?

[codeboten]

Are these defined in the spec?

I believe these fall under https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#language-specific-environment-variables