feat: deploy via GitHub Actions

[yusukebe]

Closes #473

[cloudflare-workers-and-pages]

Deploying hono with    Cloudflare Pages

Latest commit:	5229da2
Status:	✅  Deploy successful!
Preview URL:	https://84068f50.hono.pages.dev
Branch Preview URL:	https://github-actions.hono.pages.dev

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[akku1139]

Dear @yusukebe :

When I opened GitHub, I was surprised to see this Pull Request merged.
I think this is not good.

1. Description is missing.
   Despite being a very important change, there is little explanation given.

2. There is no reason to use yarn v1.
   Yarn v1 is under maintenance mode.
   Yarn v1 is no longer slower than npm.
   Yarn v4 is fast, but setting up v4 is not easy.
   Why was it bad to continue using pnpm?

3. The execution event setting for Workflow looks incorrect.
   You need to add pull_request to on.
   https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#pull_request

You should revert this pull request.