Support versions in GEL docs site

[samithaf]

We need to support versions in GEL docs so that consumers who are using older versions of GEL can still use the docs site.

Here is how Ant design doing it. Given GEL docs also now part of GitHub, most likely we need to create a new tag when we do any breaking changes and then use a pre defined tags to drive GEL docs site versions.

[samithaf]

@KateMacdonald we need a visual design for this feature.

[KateMacdonald]

Hello Samitha! Happy new year :) Let's have a chat about this one, is the intention for it to be per component? We used to have this design in previous version of GEL where we had a drop down to select the version. But the page layout has changed quite a lot since then.