support compiling set-ns and set-labels to wasm

[mengqiy]

How to compile:

$ cd functions/go/set-namespace
$ GOOS=js GOARCH=wasm go build -o set-namespace.wasm 

[yuwenma]

So cool! Is this for experimental purpose or you literally want set-namespace to be the pilot function for WASM? If it's the former, quick approval on my side. Just FYI, the latest set-namespace code is not released. It contains major changes like supporting upstream identifier. Just to mention it in case it causes noises to your experimentation. For the latter, I feel like the WASM run function may be better live in the Go SDK (But I'm totally fine if you want to have it land in this function). Just a note that before releasing set-namespace, we need to disable the warning message here.

[yuwenma]

Approved on my side. Feel free to merge or update whatever it needs.