Publish the semantic convention tool using its version

[thisthat]

The image released on docker hub should use the version contained in https://github.com/open-telemetry/build-tools/blob/master/semantic-conventions/src/opentelemetry/semconv/version.py

[Oberon00]

I think the other way round would be better: https://github.com/pypa/setuptools_scm

[jsuereth]

obsolete