Add sleuth.so target (#40965)

Add sleuth.so target (#40965)

This is a shared library target for gRPC Sleuth Python extension.

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Closes #40965

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/40965 from yousukseung:sleuth-so b6f99b496b46e8dd599b08662370d4fdf4050b9c
PiperOrigin-RevId: 825233373