Feat: Deploy both gw2-ui and react-discretize-components storybooks

[marcustyphoon]

Possible method to deploy both storybooks even though github pages only gives you one site per repository:

• Build both storybooks into subfolders of the same folder in the repo root
• Deploy the whole subfolder to github pages in an action

This, notably:

• Doesn't deploy the storybook in postpublish any more (you're deploying two packages now; "deploy when you publish one of them" doesn't really make sense)
• Does deploy the storybooks either whenever you push to main (making the storybooks reflect the dev branch instead of the current version on npm; don't love that) or only manually on workflow dispatch (ew). Can probably change that to on release in theory; that would probably involve syncing rdc and gw2-ui releases.
• Requires a change to the repository github pages settings or it'll fail (gh-pages deploys from a different branch than actions/deploy-pages).

Notable way to do this with fewer caveats: just deploy the storybooks to Cloudflare Pages instead. Could keep doing them separately in postpublish then, so long as the developer running publish has wrangler keys.

[marcustyphoon]

Actually, I just looked at the gh-pages docs and its subfolder option might be able to do this.