Automate semconv library codegen for new versions

[lmolkova]

The other thing I think would be really useful is to have a workflow convention so that generation, and ultimately creating maybe a PR, for the new version can be done by the semantic conventions repository to reduce the time that each SIG takes to release the new package. If those are stuck behind in the various languages, we'll get into the same state as we have been around the perception of instability and maturity across languages.

Originally posted by @martinjt in #551 (comment)

[lmolkova]

Many SIGs are way behind on semconv version and don't have expertise in jinja/otelsemconv code generation tools.

One way to approach it would be to have a CI pipeline that

1. is triggered by semconv version release (if possible)
2. runs in individual language repos
3. takes the new version and (using language-owned jinja templates and update script) generates new semconvs
4. sends a PR back to language repo for the review

From what I can tell, everything except step 1 is totally possible today with #550 being the only blocker.