config: add stdout exporter for log signal

[codeboten]

Problem Statement

As it was done for metric and tracing, the logging signal should support configuring a console exporter via config.

Proposed Solution

Add the following code and add unit tests as well.

	if exporter.Console != nil && exporter.OTLP != nil {
	 	return nil, errors.New("must not specify multiple exporters")
	 }

	 if exporter.Console != nil {
	 	return stdoutlog.New(
	 		stdoutlogWithPrettyPrint(),
	 	)
	 }

Additional Context

This was not possible because of a change needed in the configuration schema (open-telemetry/opentelemetry-configuration@834ae3c) which has been merged, but updating the configuration package depends on #4832 to support another change in the configuration schema.

[codeboten]

Happy to tackle this one once #4832 and #5427 have been merged