Support GitLab svg iconography in Global Nav
Now that we can invoke GitLab iconography with the doc suite, it would be great to be able to have also do that for top-level items in the Global Nav.
This would involve also having the icons remain when the left sidbar is collapsed, rather than an empty bar.
Our current global nav doesn't mirror the product's sidebar perfectly, but I think the there is enough iconography there to either:
- Match where possible. For example, CI/CD is top-level navigation in the docs and the product.
- Come up with a suitable alternative where not possible from the library of SVGs: https://gitlab-org.gitlab.io/gitlab-svgs/.