Add highlighting for Apache htaccess / conf files

### Is your feature request related to a problem? Please describe
I share mostly PHP or JS snippets for WordPress and tweaks for the `.htaccess` file. For the latter there is a syntax highlighting missing.

### Describe the solution you'd like
I found this plugin which adds a new highlighting for this:
https://www.tech-otaku.com/blogging/apache-brush-syntaxhighlighter-evolved-wordpress-plugin/

Looks like it is GPLv2 and could be added.

### Describe alternatives you've considered
Haven't found other brushes so far.

### Additional context
n/a

No repository file or test is named. Start by reviewing the linked Apache brush and the repository's existing syntax-highlighting entry points; determine how Apache .htaccess and conf snippets should be registered. Done means those snippets receive Apache syntax highlighting without regressing existing brushes.

Written by the indexing model from the issue text.