Dependabot-core: Quick access to GitHub native Dependabot dashboard

[peaceiris]

How about providing a quick link to a Dependabot dashboard for only users who have write-access to a repository?

Today, we need to click 3 times or more to go to a repository's GitHub native Dependabot dashboard as follows. This is a little bother.

1. https://github.com/peaceiris/actions-gh-pages/pulse
2. https://github.com/peaceiris/actions-gh-pages/network/dependencies
3. https://github.com/peaceiris/actions-gh-pages/network/updates

We can put a link to a dashboard on a repository README, but that is unnecessary for other users.

[feelepxyz]

@peaceiris great feedback and agreed! We'll get to this. We're currently focused on supporting private git dependencies and private registries over the next few months.