feat: Add TelemetryConfiguration and Tracer/Logger options

[cy-yun]

Description

This PR implements Phase 1 Task 1 of the Client Libraries Observability v1 design.

Changes

• Introduces TelemetryConfiguration in Google\Cloud\Core for securely parsing telemetry opt-in/opt-out configuration from environment variables (e.g. GOOGLE_SDK_PHP_TRACING_ENABLED, GOOGLE_SDK_PHP_LOGGING_ENABLED, and the legacy GOOGLE_API_ENABLE_TELEMETRY).
• Adds tracerProvider and loggerProvider configurations to ClientOptions in Google\ApiCore.
• Ensures all telemetry remains strictly opt-in by default to prevent unexpected cardinality explosions or cost increases for users.

[bshaffer]

There does not seem to be any integration here with our existing PSR-3 compliant logger. I think this difference will be confusing to our customers (and also to me, I am confused as to what the difference is already!)

Libraries exist which serve as adapters between the two (see https://packagist.org/packages/open-telemetry/opentelemetry-logger-monolog). This may be a good way to support it in the short term. A more robust solution would be to do something similar to what we already have with HttpHandler, where we have a factory which builds our own adapter class, and so we can be confident that the methods we expect exist already.

I would like to see either 1) the practical difference between loggerProvider and logger explained in the description and variable name, OR 2) a way to bridge the two (preferred)