Semconv codegen should produce different constant names if attribute is renamed _ -> ``

[lmolkova]

Code generator generates the same attribute name constant for attribute.name and attribute_name. As a result, if attribute is renamed (_ is changed to . or vice versa), the value of attribute changes, but the name stays the same.

It's ambiguous - see https://github.com/open-telemetry/semantic-conventions/issues/1031 and https://github.com/open-telemetry/semantic-conventions/issues/1118 for the discussion.

Based on https://github.com/open-telemetry/semantic-conventions/issues/1118, the semconv recommendation would be to:

• Remove _ when generating any constants in the code (fields, methods, class names, etc)
• Semconv will prohibit attribute renames that are limited to adding/removing _

This PR demonstrates the result of such naming policy change.