Add mostly-unchanged Helm chart from k8s-at-home

- Add the chart from k8s-at-home with some modifications
- Add the Apache 2.0 license to the new charts/paperless-ngx
  subdirectory, the license under which the chart was distributed by
  k8s-at-home. I believe the chart will have to maintain this license.

- Update the maintainers section and contact information to point to
  Paperless-ngx.
- Regenerate the README (using helm-docs)

- Add a GitHub actions configuration to publish the chart using GitHub
  pages. This makes the GitHub Pages page rendered by this repository
  usable as a Helm repository, without affecting potential future uses
  of the Pages site.

These are in response to discussion #1790.

charts/paperless-ngx/.helmignore

@@ -0,0 +1,26 @@
+# Patterns to ignore when building packages.
+# This supports shell glob matching, relative path matching, and
+# negation (prefixed with !). Only one pattern per line.
+.DS_Store
+# Common VCS dirs
+.git/
+.gitignore
+.bzr/
+.bzrignore
+.hg/
+.hgignore
+.svn/
+# Common backup files
+*.swp
+*.bak
+*.tmp
+*~
+# Various IDEs
+.project
+.idea/
+*.tmproj
+.vscode/
+# OWNERS file for Kubernetes
+OWNERS
+# helm-docs templates
+*.gotmpl