Add link from GitLab Next badge to next.gitlab.com

Problem to solve

Since a couple of days, we started showing the Next badge when using the Canary infrastructure.

There have been a lot of questions from users both internally and externally about what that means.

Examples: https://gitlab.slack.com/archives/C0AR2KW4B/p1557158462422500?thread_ts=1557158462.422500 https://gitlab.slack.com/archives/C4XFU81LG/p1557163386002900

Intended users

Everybody who uses the Canary infrastructure.

Proposal

As first step to make this more understandable and add visibility, we could add a link from that badge to the next.gitlab.com page.