Enable ProcessResourceDetector by default

Is your feature request related to a problem?

It would be helpful to have by default the python version of traced services. The python version is contained in process.runtime attribute: https://opentelemetry.io/docs/specs/semconv/resource/process/

Describe the solution you'd like

Currently the ProcessResourceDetector that is providing the information is not enabled by default but can be enabled via OTEL_EXPERIMENTAL_RESOURCE_DETECTORS environment variable.

From opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py:

       otel_experimental_resource_detectors = environ.get(
            OTEL_EXPERIMENTAL_RESOURCE_DETECTORS, "otel"
        ).split(",")

        if "otel" not in otel_experimental_resource_detectors:
            otel_experimental_resource_detectors.append("otel")

We see that we already enable the OTELResourceDetector even if it the attributes are experimental.
So I'd like to add the ProcessResourceDetector enabled by default with something like:

         otel_experimental_resource_detectors = environ.get(
-            OTEL_EXPERIMENTAL_RESOURCE_DETECTORS, "otel"
+            OTEL_EXPERIMENTAL_RESOURCE_DETECTORS, "otel,process"
         ).split(",")

Describe alternatives you've considered

Alternatively if we are worried that sensitive data may be shared from process args we can add by default only a detector providing the process.runtime attributes.

Additional context

Start in opentelemetry-sdk/src/opentelemetry/sdk/resources/init.py and read how OTEL_EXPERIMENTAL_RESOURCE_DETECTORS is parsed and how ProcessResourceDetector provides process.runtime. Check how the existing default detector behavior is covered, then verify that process.runtime is enabled by default while the environment-variable configuration remains usable.