Publish Windows releases (cloud-agent)

Related to cdr/code-server#1397.

This will make it possible to run --link with Windows out of the box.

## A current workaround (for --link on Windows) is to build it manually:
1. Install go
2. Install code-server via yarn/npm (if you haven't already)
3. Clone this repo:
```console
git clone https://github.com/cdr/cloud-agent.git
cd cloud-agent
```
4. Build cloud-agent and move to the global module.

Replace `v0.2.3` with the latest cloud-agent [release tag](https://github.com/cdr/cloud-agent/releases):
```console
# if you installed via yarn
go build -v -o $(yarn global dir)/node_modules/code-server/lib/coder-cloud-agent.exe -ldflags "-X go.coder.com/cloud-agent/internal/version.Version=v0.2.3"
# if you installed via npm
go build -v -o $(npm config get prefix)/node_modules/code-server/lib/coder-cloud-agent.exe -ldflags "-X go.coder.com/cloud-agent/internal/version.Version=v0.2.3"
````