Should the SemanticAttributes & ResourceAttributes generated classes be moved out of this repository?

[jkwatson]

The problem(s):

1. With evolving semantic conventions, currently a user can only depend on a single version of the SemanticAttributes class, and that may be incompatible with the version being used by another library. Even with schema evolution, these attributes classes could be incompatible from an API perspective. Hence, we might want to change the naming scheme of the artifacts to include the version of the spec that they were generated from.
2. Much like we pulled the generated protobuf bindings out of this repository, so users don't need to depend on the possibly mismatched, or delayed releases, perhaps we should pull out the generated semantic convention constants into a separate repository with a different versioning scheme.