 x/build: add LUCI wasip1-wasm32_wazero builder

As part of the work on the wasm32 architecture, we'd like to add a new builder for running the wasip1 tests. This builder will need to have wazero installed and set the following environment variables:

```
GOOS=wasip1
GOARCH=wasm
GOWASIRUNTIME=wazero
PATH=$PATH:/workdir/go/misc/wasm
GO_DISABLE_OUTBOUND_NETWORK=1
```

CC @dmitshur @golang/wasm 