Support syntax-highlighting Dockerfiles

[xfbs]

Problem

Currently, the version of highlight.js shipped with mdBook does not support syntax highlighting Dockerfiles.

Proposed Solution

Add dockerfile to the list of default highlight.js languages

Notes

No response

[szabgab]

I am not sure if the maintainers would want to add Dockerfile support and if when, you could solve this issue in your book following the advice I wrote here: #2498