Releasing Devtools

This is for maintainers only.

Pre-requisites

Make sure you have publishing rights to the @vue/devtools and @vue/devtools-api npm packages (check with npm owner ls @vue/devtools). If not, ping @yyx990803 for publishing permission.
Sign up and create API keys for Firefox Addons. Create .amo.env.json in project root with the keys:
```
{
  "apiKey": "...",
  "apiSecret": "..."
}
```
Run npm run release:beta.

If it completes without error, it should have published the necessary npm packages.

In addition, this should create the following files:

dist/chrome.zip

This is the packed chrome extension which should be uploaded via Chrome Web Store developer dashboard. Note the items are under the vuejs-dev publisher group. We current have two extensions, one for beta (currently Vue 3 only) and one for stable (Vue 2 only). We will eventually replace the stable with this branch once it supports both Vue 2 and Vue 3, but for now the Vue 3 supporting version should be published under the beta channel.
distvue.js_devtools-x.x.x.zip

Similarly, the stable version of the Firefox Addon can be updated here. But before then, we simply publish it as a pre-signed zip file. It should be added as a binary to the GitHub release.

The release should have updated the versions of a few package.json files. Add and commit them, then add a git tag in the format of v6.x.x. Push both the commit and the tag to GitHub, and publish the release on GitHub (we should probably automate this with local script + GitHub actions).