Introduce ESM testing strategy

[pichlermarc]

Is your feature request related to a problem? Please describe

In the @opentelemetry/instrumentation package, we added experimental ESM support a while ago (open-telemetry/opentelemetry-js#3698). As more and more users started using this, the lack of ESM-releated testing became apparent. A high-priority bug that's present in a large number of instrumentations causes applications to crash as wrapping ES modules fails.

• pg: cannot instrument an ESM-imported pg #1693
• pg instrumentation crashes when using ES module. #1588
• Pino instrumentation fails when using ES modules #1587
• instrumentation-fastify fails to initialise if "type" is set to "module" in package.json #1519
• ioredis: cannot instrument an ESM-imported ioredis #1692

There have been PRs opened to address this; however, as we don't test for ESM, it is hard to verify fixes and catch regressions.

Describe the solution you'd like to see

We should start testing if instrumentations also work with ESM. This issue tracks

• documenting an ESM testing strategy for existing packages
• implementing the suggested tests in at least two instrumentation packages
• adding a step in the unit tests workflow to run the ESM tests

[pichlermarc]

I've been experimenting a bit, and we may be able to re-use the existing mocha tests in ESM mode by using the ts-node/esm loader and chaining it with import-in-the-middle to get full coverage.

At the moment one thing preventing us from doing so is that once I add @opentelemetry/instrumentation/hook.mjs as a loader, the require.main === module check in ./node_modules/mocha/lib/cli/cli.js fails and mocha exits without running tests. I think this may be related to how import-in-the-middle works, so I opened nodejs/import-in-the-middle#34.