Inconsistent console exporter behavior/documentation

Is your feature request related to a problem?
Not really a problem, but an observation.

Code discrepancies:

• OpenTelemetry\SDK\Logs\Exporter\ConsoleExporter depends on being created by ConsoleExporterFactory to create the appropriate stream transport, otherwise it's not actually exporting to the consol
• OpenTelemetry\SDK\Metrics\MetricExporter\ConsoleMetricExporter uses echo for output (the only time echo is used anywhere in the SDK)
• OpenTelemetry\SDK\Trace\SpanExporter\ConsoleSpanExporter depends on SpanExporterFactoryInterface in the same manner as the Log exporter

Documentation discrepancies:

Referencing this otel.io page:

• Under "Instrumentation setup>Initialize the SDK" the example instrumentation.php creates each exporter by configuring the stream transport directly
• Under "Traces>Span Processor" the ConsoleSpanExporterFactory is used
• Under "Metrics>Setup" the ConsoleMetricExporterFactory is used
• Under "Logs>Setup" the stream transport is configured directly

Describe the solution you'd like

• Update ConsoleMetricExporter to use a transport instead of echo
• Update all three exporters to have a default stream transport targeting php://stdout so they are functionally "console" exporters even without the factory
• Remove the (then redundant) default transport from the factories
• Update the documentation to use the console exporter factory in all instances

Describe alternatives you've considered
Checked for any related issues, did not see any.

Additional context
None.

Start by reading ConsoleExporter, ConsoleMetricExporter, ConsoleSpanExporter, and their corresponding factory classes to compare transport and output handling. Review the referenced instrumentation, span processor, metrics, and logs documentation, then verify that all exporters consistently target php://stdout and that the documentation consistently uses the console exporter factories.