fix: minor fixes related to release (#5732)

* fix: use * for test plugin engines

This removes the need to update this version with every version change.

* refactor: use npm-package in release assets

This adds a new job to `release.yaml` to upload the `npm-package` to the
release assets which will also allow us to download it in the
`publish.yaml` workflow.

* docs: update release instructions

* fixup!: use package.tar.gz

test/unit/node/test-plugin/package.json

@@ -3,7 +3,7 @@
   "name": "test-plugin",
   "version": "1.0.0",
   "engines": {
-    "code-server": "^4.8.1"
+    "code-server": "*"
   },
   "main": "out/index.js",
   "devDependencies": {