refactor(openai): rename functions to tools

[achang97]

Note: I manually added the TOOLS fields to attributes to get the tests to pass.

• [x] I have added tests that cover my changes.
• [ ] If adding a new instrumentation or changing an existing one, I've added screenshots from some observability platform showing the change.
• [ ] PR name follows conventional commits format: feat(instrumentation): ... or fix(instrumentation): ....
• [ ] (If applicable) I have updated the documentation accordingly.