feat(config): wire id_generator from declarative configuration to TracerProvider

[aman-panjwani]

Description

Wires the id_generator field from declarative configuration to TracerProvider, closing the parity gap with Java/JS SDKs. Depends on #5333 (merged) which added IdGenerator to models.py.

Fixes #5334

Changes

• Added _ID_GENERATOR_REGISTRY and _create_id_generator in _tracer_provider.py using the existing _resolve_component helper
• Built-in random resolves to RandomIdGenerator
• Unknown names load from the opentelemetry_id_generator entry point group (same group OTEL_PYTHON_ID_GENERATOR uses today)
• Threaded id_generator through create_tracer_provider - absent config passes None so the SDK applies its own RandomIdGenerator default

Tests Added

• test_absent_id_generator_uses_sdk_default - omitted config → SDK default RandomIdGenerator
• test_builtin_random_id_generator - built-in random → RandomIdGenerator
• test_plugin_id_generator_loaded_via_entry_point - unknown name → loaded from opentelemetry_id_generator entry point group
• test_unknown_id_generator_raises_configuration_error - unknown name with no matching entry point → ConfigurationError
• test_empty_id_generator_raises_configuration_error - empty config → ConfigurationError

Type of change

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

How Has This Been Tested?

• Ran tox -e ruff - linter and formatter passing

Does This PR Require a Contrib 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