opentelemetry-sdk: activate instrumentors from declarative config (#5372)

* opentelemetry-sdk: implement instrumentation.python declarative config support

Add configure_instrumentation() to activate instrumentors listed under
instrumentation/development.python in a declarative config file. Each
key is resolved via the opentelemetry_instrumentor entry point group and
instrument(**opts) is called with the supplied options. An enabled: false
value suppresses a library without raising; unknown entry points and
instrumentor failures are logged without stopping the others.

Wire configure_instrumentation() into configure_sdk() so the python
section is applied alongside providers on the declarative config path.

Fixes #5361

Assisted-by: Claude Sonnet 4.6

* opentelemetry-sdk: normalize slash in YAML keys during dict-to-dataclass conversion

Schema keys like "otlp_file/development" use "/" as a namespace separator
for development/experimental features. Python dataclass field names cannot
contain "/" so they use "_" (e.g. "otlp_file_development"). Without
normalization, the key falls through to additional_properties and triggers
an entry-point lookup for "otlp_file/development" (which doesn't exist),
rather than using the dedicated _create_otlp_file_development_span_exporter
factory function.

* opentelemetry-sdk: validate instrumentation opts via config_dataclass

If an instrumentor class exposes a config_dataclass attribute, the raw
YAML options are run through _dict_to_dataclass before instrument() is
called. This reuses the same type-coercion pipeline used for SDK
component configuration so instrumentors declare a typed dataclass
schema and the SDK handles the rest.

Instrumentors without config_dataclass continue to receive options
unchanged, preserving backwards compatibility.

* refactor: inline _coerce_opts into configure_instrumentation

* refactor: rename _instrumentation to instrumentation, use from-imports, expand slash-normalization comment

* changelog: add fragment for PR 5372

* fix(ci): fix pylint and ruff failures in instrumentation files

- Rename walrus variable `v` to `value` (pylint C0103)
- Add pylint disable=no-self-use at class level in test file (pylint R6301)
- Move `instrumentation` import after `_tracer_provider` in _sdk.py (ruff I001)
- Convert `import logging/dataclasses/unittest` to from-imports
- Apply ruff format to reformatted lines

* fix(ci): move pylint disable inside class body so it applies to methods

* refactor: rename config_dataclass attribute to configuration

* ci: retrigger

* fix: address review comments on instrumentation declarative config

- Add inspect.isclass + is_dataclass guard before using the
  configuration attribute, so non-dataclass values are silently ignored
- Skip instrument() when the instrumentor is already active to avoid
  duplicate-instrumentation warnings when opentelemetry-instrument and
  declarative config are both in play
- Add Instrumentation section to docs/sdk/configuration.rst with
  instrumentation/development.python YAML example
- Add instrumentation/development example to the declarative-config
  example otel-config.yaml and README

* fix: use from inspect import isclass instead of import inspect

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Co-authored-by: Mike Goldsmith <goldsmith.mike@gmail.com>
Co-authored-by: Leighton Chen <lechen@microsoft.com>