Enable function plugin mechanism

[webup]

This task is to implement this proposal, which has already been completed by Go Functions Framework (check out this sample).

Since Node.js has the capacity to load module files at runtime, the implementation could be different from that in Go FF, but please do make sure we need to achieve the same function using experience for our end users.

🐱 type: feature, priority: high

[YADROOKIE]

/assign