Setting built-in sampler with auto-instrumentation fails with Failed to initialize custom sampler due to it missing from entry points

[matej-g]

Previously also reported in open-telemetry/opentelemetry-operator#1468, but I believe this needs to be fixed in the SDK.

Describe your environment
Python 3.9
MacOS 12.6.2
OTEL version latest release (1.15.0/0.36b0)

Steps to reproduce

• Set env var OTEL_TRACES_SAMPLER to one of the built-in sampler values, e.g. OTEL_TRACES_SAMPLER=always_off
• Run any application with auto-instrumentation as instructed in https://opentelemetry.io/docs/instrumentation/python/automatic/agent-config/
• Observe the warning message, e.g. Using default sampler. Failed to initialize custom sampler, always_off: Requested component 'always_off' not found in entry points for 'opentelemetry_traces_sampler'

What is the expected behavior?
The agent should use the built-in sampler.

What is the actual behavior?
The agent complains about the sampler missing from entry points and falls back to using the default sampler.

Additional context
I believe this should be fixed by adding the samplers to entry points in opentelemetry-sdk. Some additional code change might be necessary as well, e.g. the sampler arg does not seem to be handled correctly (should be float not str), there is a mix between Callable and Sampler objects in the list of built-in samplers.

[danw-mpl]

Ran into this one myself today. Hopefully that PR can go in soon. 🚀