chore: add semconv gem to relevant gemspecs and require explicitly

[ericmustin]

Followup for https://github.com/open-telemetry/opentelemetry-ruby/pull/1083

We should include a loose semconv gem dependency and explicitly require in the module during instrumentation loading, when it's being used in instrumentation.

Since the -sdk takes a loose semconv dependency this has not caused errors when the SemanticConventions constant gets used by instrumentations, but technically these instrumentations can be used outside the SDK and must not hold any hard SDK Dependency, so it's necessary that we add the semconv gem to their gemspec

Note: Trilogy already has a semconv gem dependancy in it's gemspec

(alternatively, should we just include this in -base?)

[plantfansam]

Hello, and thank you for your contribution!

We recently split Ruby instrumentation out into the opentelemetry-ruby-contrib repo.

This PR is related to instrumentation, so we'll need you to re-open it against opentelemetry-ruby-contrib. Sorry for the inconvenience!

To do that, you can:

1. Create a fork of opentelemetry-ruby-contrib and copy the git url
2. In your opentelemetry-ruby repo, run git remote add tmp-contrib <your-fork-git-url>
3. git push tmp-contrib your-branch-name
4. Open a new PR in contrib (feel free to just copy/paste your original PR description there)
5. Close your open PR in this repo with a comment that links to your new PR in contrib
6. Delete your tmp-contrib remote from opentelemetry-ruby (git remote rm tmp-contrib)
7. git clone your opentelemetry-ruby-contrib fork, check out your branch, and make all changes in that repo from now on!

Sorry again for the inconvenience, and thank you for contributing!