GitLab UI's font-family does not match GitLab's

In !832 (merged), we noticed that the font-family property in GitLab UI isn't the same as the one in GitLab, which can lead to inconsistencies depending on the environment.

@markrian noticed the issue running GitLab UI on Ubuntu 18.04.3:

alert

tabs

---

font-family in gitlab-ui:

-apple-system, system-ui, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";

font-family in gitlab:

-apple-system, system-ui, "Segoe UI", Roboto, "Noto Sans", Ubuntu, Cantarell, "Helvetica Neue", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";

Should we update the font-family in GitLab UI to match GitLab's fallback chain?