Add SLES to OS list in Installation page

[Kinda spinned off from https://gitlab.com/gitlab-com/www-gitlab-com/issues/1074#note_27579894]

From 9.1 onwards, we are providing EE packages for SLES - SUSE Linux Enterprise Server - (Related issue - https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1730 ). So, SLES has to be added to https://about.gitlab.com/installation/ page where we list other OSs/packages. The thing to note is, we are not providing a CE package for it.

/cc @psimyn (Because you recently did the revamp of that page), @luke and @eliran.mesika

@psimyn @luke we can try adding this if you provide us with the image we can use? If we get stuck we can ask for further help.

@marin based on my quick research there isn't a logo specifically for SLES - SUSE Linux Enterprise Server. So we can use the SUSE logo and state SLES - SUSE Linux Enterprise Server in the title text below, assuming it will be a card in one of the lower sections, and not in the Omnibus table at the top of the page.

mentioned in issue #1336 (closed)

@balasankarc would you want SLES listed in the top section? This will be easier to add after https://gitlab.com/gitlab-com/www-gitlab-com/issues/1336 is done to simplify tabs and display

@psimyn SLES should be listed next to other OSs we have - like Debian, Ubuntu, CentOS etc.

PS: SLES is EE-only. We don't need it in CE page, if there will be one.

@luke how can we best support these platforms which are only available in either CE or EE? For example RPi is only supported on CE and SLES is only supported on EE.

I imagine we will still want the tile to show, since you pick before you select the edition. But can we have more of a message if you pick one that is unavailable to say something like "Raspberry Pi support is exclusive to Community Edition" or similar?

assigned to @luke

@joshlambert WDYT? We could gray out the Enterprise Edition text and show a tooltip on hover.