Blog post should be categorized by Topics

还没有人认领这个 Issue。

**Describe the solution you'd like**
We are able to apply tags to blog posts but users may also want to search by general topics. These topics will also allow us to create a featured carousel for each topic on the landing page. Users can search by topic and then refine search using tags. Eventually, there may be a whole page dedicated to just that topic?

These categories will not be user-created so they could be created as an enum class.

Proposed Topic:
STL
KC
PHIL
Games
Tech
Interview Insights
Events
Contributors/Bios
OpenSource

**Describe alternatives you've considered**

**Additional context**
See recording for 2/17/22 for our mini brainstorming on this idea.

未指定文件、测试或入口点。检查现有的标签、搜索和落地页流程，然后确定固定主题列表和主题筛选应如何工作；完成的标准是：帖子可以分配到提议的主题、按主题搜索、使用标签进一步筛选，并用于主题轮播。

由索引模型根据 Issue 内容生成。