Consider moving semantic conventions out of the API

[carlosalberto]

A few components setting Semantic Conventions attributes are defined in the API, such as this one - however, as semantic conventions are not stable yet, it may be a good idea to put them in their own package/artifact.

[nachoBonafonte]

I will bring this to the SIG meeting, and talk about the options

[nachoBonafonte]

Hi @carlosalberto, we are not very sure what are you meaning here, just deleting that out-of-spec code and documenting the experimental status of Semantic conventions or something more. Is there a reference spec that we could use?