Support SkyWalking as one default plugin for tracing

[webup]

This task is one follow-up of #46, in which we'd like to enable function tracking by support SkyWalking as one of built-in plugins in Node.js Functions Framework.

The implementation of SkyWalking plugin should comply with this proposal, and make sure this sample still work well at user end.

🐱 type: feature

[YADROOKIE]

/assign

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 60 days. It will be closed in the next 7 days unless it is tagged (pinned, good first issue, help wanted or triaged/resolved) or other activity occurs. Thank you for your contributions.

[github-actions]

This issue has been automatically closed because it has not had activity in the last 67 days. If this issue is still valid, please ping a maintainer and ask them to label it as pinned, good first issue, help wanted or triaged/resolved. Thank you for your contributions.