Use categories to identify products on each content page

[mich-elle-luna]

This PR adds a table at the top of every page with a category column that is color coded for the applicable products. Let me know what you think.

https://redis.io/docs/staging/categories/operate/
https://redis.io/docs/staging/categories/operate/oss_and_stack/install/install-redis/install-redis-from-source/

[andy-stark-redis]

@mich-elle-luna Great idea to add category info to the page and I think having it right under the brief description line is the ideal position :-) Just a few thoughts about this:

1. The table seems too big to me (gives the impression of a warning/deprecation message or something at first sight). You could shrink it down quite a bit and maybe reduce the text to just "Applies to:" or leave that out altogether and just have the categories. One possible way to do it might be like the badges that you sometimes see on Github readme pages (eg, https://github.com/redis/redis-py/tree/master) but with just the category names?
2. (Relates to point 1) Should we consider expanding this in the future to a wider range of categories? I'm thinking of things like tools, security... could be open-ended. Maybe we want a layout that allows for this even if we don't implement it yet?
3. Should we add links to the category names? It could be a good way to direct the user to an overview page, say if they come in from a Google search.
4. The info doesn't seem to display on index pages, even when they have content as well as the section listing.

[mich-elle-luna]

Ok @andy-stark-redis I worked on the styling, let me know if this looks good to you or if you have more feedback. I think I will wait to add linking and the categories list/index pages in a separate PR because this first part could actually help people already. But, I will work on that part next. Thanks!

[andy-stark-redis]

@mich-elle-luna I'd say that's looking quite nice now :-) Using a table with rounded ends but straight dividers between categories looks really neat. The only thing I would note is that the categories appear on almost all of the appropriate pages but not absolutely all (eg, Redis Insight landing page). This is because the category metadata isn't in these pages, and not down to a layout issue. However, if we introduce these categories then I would say we really need to check they appear everywhere they should. As with the links, this probably needs a separate PR to check for missing metadata and fix it. Also, I'm wondering if there's a way to automate checking/suggesting categories in all the docs based on keywords or something?