as recommended by @alexmurray to keep consistency with other snaps; see
https://forum.snapcraft.io/t/system-files-and-personal-files-request-for-hugo/30598/2

One closer step towards fixing #6226

as recommended by @alexmurray to keep consistency with other snaps; see
https://forum.snapcraft.io/t/system-files-and-personal-files-request-for-hugo/30598

I neglected to make the rename of system-gitconfig → etc-gitconfig and
user-gitconfig → gitconfig to the apps.plugs section in commit fd3953c,
hence this commit to fix the store upload scan failure:

  interface 'system-gitconfig' not found in base declaration
  interface 'user-gitconfig' not found in base declaration
  unknown plugs interface name reference 'system-gitconfig'
  unknown plugs interface name reference 'user-gitconfig'

Special thanks to Alex Murray and Igor Ljubuncic for approving the
system-files and personal-files request for Hugo.

Fixes #6226

Fixes #10053

e5aa641 remove erroneous foo
8307b47 Add hl_inline to highlight function documentation
8517b02 update GitHub 404 docs URL to prevent redirect
5c52c27 remove aerobatic.com
3eb1795 Update syntax-highlighting.md
00cbe3f Check for nil Chroma .Aliases
4541651 netlify: Hugo 0.101.0
d5dcd15 docs: Regen docshelper
4785e99 common: Add hugo.GoVersion
e679f1b resources/page: Add :slugorfilename attribute
f2cc72a Update spellcheck.yml (#1755)

git-subtree-dir: docs
git-subtree-split: e5aa641

And add some assertions.

Adds the citeproc filter to the pandoc converter.

There are several PRs for it this feature already. However, I think
simply adding `--citeproc` is the cleanest way to enable this feature,
with the option to flesh it out later, e.g., in #7529.

Some PRs and issues attempt adding more config options to Hugo which
indirectly configure pandoc, but I think simply configuring Pandoc via
Pandoc itself is simpler, as it is already possible with two YAML
blocks -- one for Hugo, and one for Pandoc:

    ---
    title: This is the Hugo YAML block
    ---
    ---
    bibliography: assets/pandoc-yaml-block-bibliography.bib
    ...
    Document content with @citation!

There are other useful options, e.g., #4800 attempts to use `nocite`,
which works out of the box with this PR:

    ---
    title: This is the Hugo YAML block
    ---
    ---
    bibliography: assets/pandoc-yaml-block-bibliography.bib
    nocite: |
      @*
    ...
    Document content with no citations but a full bibliography:

    ## Bibliography

Other useful options are `csl: ...` and `link-citations: true`, which
set the path to a custom CSL file and create HTML links between the
references and the bibliography.

The following issues and PRs are related:

- Add support for parsing citations and Jupyter notebooks via Pandoc and/or Goldmark extension #6101
  Bundles multiple requests, this PR tackles citation parsing.

- WIP: Bibliography with Pandoc #4800
  Passes the frontmatter to Pandoc and still uses
  `--filter pandoc-citeproc` instead of `--citeproc`.
- Allow configuring Pandoc #7529
  That PR is much more extensive and might eventually supersede this PR,
  but I think --bibliography and --citeproc should be independent
  options (--bibliography should be optional and citeproc can always be
  specified).
- Pandoc - allow citeproc extension to be invoked, with bibliography. #8610
  Similar to #7529, #8610 adds a new config option to Hugo.
  I think passing --citeproc and letting the users decide on the
  metadata they want to pass to pandoc is better, albeit uglier.