Allow creating WASM VM context with environment variables

[drewcorlin1]

I'm using proxytest.NewWasmVMContext() to create a WASM VM to run tests against. The system under test is deployed as an Istio WasmPlugin. My plugin sets response headers on requests that flow through my istio proxy. Some of those headers come from environment variables available to the istio-proxy (envoy instance) that I'm exposing via https://istio.io/latest/docs/reference/config/proxy_extensions/wasm-plugin/#VmConfig. This works correctly in production (and in my code I just use os.Getenv no problem), but in my test I'm unable to configure environment variables for the WASM VM in my test.

I've also tried using proxyTest.NewEmulatorOption().WithVMConfiguration() to set the VM Config but that doesn't seem to work.

I think this means allowing NewWasmVMContext to be configured with environment variables that can then be passed to wazero.NewModuleConfig() via .WithEnv() on ModuleConfig.

https://github.com/proxy-wasm/proxy-wasm-go-sdk/blob/main/proxywasm/proxytest/wasmwrapper.go#L103

[drewcorlin1]

This could look something like this change to NewWasmVMContext. I'm no go expert, this is me hacking things together and I recognize this is a breaking change so I'm sure there are better alternatives. I certainly welcome feedback on this approach and I'd be happy to make a contribution if this sort of change is welcome

type WasmVmConfig struct {
	EnvironmentVariables map[string]string
}

func NewWasmVMContext(wasm []byte, wasmVmConfig WasmVmConfig) (WasmVMContext, error) {
	ctx := context.Background()
	r := wazero.NewRuntime(ctx)

	_, err := wasi_snapshot_preview1.Instantiate(ctx, r)
	if err != nil {
		return nil, err
	}

	err = exportHostABI(ctx, r)
	if err != nil {
		return nil, err
	}

	compiled, err := r.CompileModule(ctx, wasm)
	if err != nil {
		return nil, err
	}

	wazeroconfig := wazero.NewModuleConfig().WithStdout(os.Stderr).WithStderr(os.Stderr)

	if (wasmVmConfig.EnvironmentVariables != nil) {
		for key, value := range wasmVmConfig.EnvironmentVariables {
			wazeroconfig = wazeroconfig.WithEnv(key, value)
		}
	}
    // ..
}