Issue a warning for examples without title

[bastelfreak]

Use Case

puppet-strings supports examples likes:

# @example this is the title
#   insert puppet code here
#

puppet-strings ignores missing titles and will then add a bunch of #### into the REFERENCE.md.

Describe the Solution You Would Like

It would be nice if puppet-strings could issue a warning/error if the title for an example is missing and if that could be used in a rake task to validate the puppet files.

Describe Alternatives You've Considered

This is based on https://github.com/voxpupuli/puppet-lint-param-docs/ but I think it would make more sense to have this feature within puppet-strings

Additional Context

Add any other context or screenshots about the feature request here.

[genebean]

It sure would be nice for puppet-strings to be able to be told to fail for warnings (similar to how puppet-lint can be configured) and for undocumented bits. We are currently having to work around the limitations of puppet-strings with this in a GitHub Action:

set -e
documentation=$(pdk bundle exec puppet strings generate --format markdown)
if [ $(echo $documentation | grep -Ec "[1-9]+ undocumented|\[warn\]") -gt 0 ]; then
  echo "Please resolve documentation issues detected below:"
  echo "$documentation"
  exit 1
fi