refactor(ci): clean up npm workflows (#4786)

This extracst the publish on npm workflow from ci.yaml and adds a new workflow
called `npm-beta.yaml`.

Now we have three workflows that publish to npm.
- `npm-beta.yaml` only runs on pushes and merges into `main`
- `npm-dev.yaml` only runs on PRs into `main` with approval from
  code-server-reviewers team
- `npm-brew.yaml` only runs on releases

This should fix problems we had previously where anyone could open a PR and
publish under the code-server namespace. It also separates out the workflows
based on environment and when they should run.

.github/workflows/npm-brew.yaml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - name: Publish npm package with PR number and commit SHA
+      - name: Publish npm package and tag with "latest"
         run: yarn publish:npm
         env:
           ENVIRONMENT: "production"