added custom frontmatter for topics, override for about/history

[stockholmux]

Description

Up to this point, the frontmatter of all documentation topics were fixed and generated en mass by a loop.

This PR accomplishes three things:

1. It allows for custom front matter on documentation topics. Adding a file to /build/custom-frontmatter/topics/ with a filename the correlates with the the topic slug will replace the generate frontmatter with the customer frontmatter.
2. It overrides the frontmatter for /topics/history to allow for an alias for the /about/ page, preserving the existing URL with a forward.
3. It removes the old /about/ page

TL;DR: /about/ forwards to /topics/history/ and there is a now a way that we can make further customizations to the frontmatter in the documentation topics on the website side.

Issues Resolved

Closes #19

Check List

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the BSD-3-Clause License.