Reuse PortForwarder container if it is running

[cristianrgreco]

Resolves #677. Closes #678

The current implementation of the PortForwarder relies on a singleton to ensure that multiple forwarders are not started at the same time. The idea is that there is one forwarder per session.

The reliance on a singleton falls apart when test suites run in different processes. Similar then to the reaper implementation, we now check for the existence of a forwarder container and reuse it if it exists, instead of creating a new one. This resolves the conflicts reported in #677. This PR additionally handles the case where we attempt to forward the same port multiple times, by querying the forwarder container for its bound ports on error and skipping if already bound.

To do:

• Remove duplication, e.g. getting network settings. Consider moving to container/network client
• See if we can reset just the port forwarder module instead of all modules within the Jest test
• See if we can unify the port forwarder test suites

[netlify]

✅ Deploy Preview for testcontainers-node ready!

Name	Link
🔨 Latest commit	5847e1b
🔍 Latest deploy log	https://app.netlify.com/sites/testcontainers-node/deploys/6560a14651846c00088febe9
😎 Deploy Preview	https://deploy-preview-680--testcontainers-node.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.