Public API for setting logger/tracer configuration programmatically

What

Provide a public API to set logger (and, for consistency, tracer) configuration programmatically at runtime, so users can enable/disable a logger or adjust its config without relying on the private _-prefixed API.

Background

PR #5380 wires Logger.enabled() to consult LoggerConfig.is_enabled. The configuration itself is already settable programmatically today, but only through private API:

• _LoggerConfig(is_enabled=...)
• LoggerProvider._set_logger_configurator(logger_configurator=...) / the _logger_configurator constructor argument

This came up in review on #5380 (https://github.com/open-telemetry/opentelemetry-python/pull/5380#discussion_r3715217160), where the question was raised that it should eventually be possible to set this via a public API.

Why this is a separate change

The tracer side is the template for this code and is also still private (_TracerConfig, TracerProvider._set_tracer_configurator). Promoting logger config to a public API in isolation would diverge the two signals. This should be a deliberate, consistent cross-signal decision (traces and logs, and any future signal), so it does not belong inside the enabled() PR.

Proposed scope

• Decide on the public surface for setting config on a provider (configurator callable vs. direct config object, naming).
• Apply it consistently to both TracerProvider and LoggerProvider.
• Keep the existing private entry points working (or alias them) during the transition.

cc @aabmass @herin049

Start by reviewing the private _LoggerConfig, LoggerProvider._set_logger_configurator, _logger_configurator, _TracerConfig, and TracerProvider._set_tracer_configurator entry points, along with the discussion in PR #5380. Define a consistent public configuration surface for both providers, preserve the existing private entry points during transition, and verify that the resulting API covers logger and tracer configuration.