Support OTEL_LOG_LEVEL for internal logger

[hariharan077]

Fixes #1059.

What changed

• Configure the OpenTelemetry internal logger (opentelemetry) from OTEL_LOG_LEVEL during SDK setup.
• Default unset, empty, and invalid values to INFO; invalid values also emit a warning.
• Add regression coverage for configured, default, empty, invalid, and child-logger propagation behavior.

Verification

• Reproduced the issue locally before the fix: OTEL_LOG_LEVEL=debug left the opentelemetry logger at NOTSET.
• .tox/py310-test-opentelemetry-sdk/bin/python -m pytest opentelemetry-sdk/tests/test_configurator.py::TestInternalLogLevel
• .tox/py310-test-opentelemetry-sdk/bin/python -m pytest opentelemetry-sdk/tests/test_configurator.py::TestConfigurator opentelemetry-sdk/tests/test_configurator.py::TestLoggingInit
• .tox/py310-test-opentelemetry-sdk/bin/python -m pytest opentelemetry-sdk/tests/test_configurator.py
• uv run ruff format --check opentelemetry-sdk/src/opentelemetry/sdk/_configuration/__init__.py opentelemetry-sdk/tests/test_configurator.py
• uv run ruff check opentelemetry-sdk/src/opentelemetry/sdk/_configuration/__init__.py opentelemetry-sdk/tests/test_configurator.py
• uv run tox -e py310-test-opentelemetry-sdk
• uv run tox -e lint-opentelemetry-sdk
• uv run towncrier build --draft --version Unreleased

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: hariharan077 / name: hariharan077 (428b884, ea76185)

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