grm showconfig do not show boolean configurations when value is `false`

[AdmiringWorm]

Description

When running gitreleasemanager showconfig I expected to see all of the configurations (both configured and available) in the yaml file. However, I found that grm would not display any of the boolean configuration values when the value is set to false.

Steps to reproduce

1. Set the configuration value create.include-footer to false.
2. Run gitreleasemanager showconfig
3. Look at the output

Actual output

for a default configuration with only create.include-footer changed to false.

create:
  footer-heading: ''
  footer-content: ''
  milestone-replace-text: ''
  sha-section-heading: SHA256 Hashes of the release artifacts
  sha-section-line-format: '- `{1}      {0}`'
export:
  created-date-string-format: ''
  regex-text: ''
issue-labels-include:
- Bug
- Duplicate
- Enhancement
- Feature
- Help Wanted
- Improvement
- Invalid
- Question
- WontFix
issue-labels-exclude:
- Internal Refactoring
issue-labels-alias: []

Expected output

With the same configuration

create:
  include-footer: false # this is missing
  footer-heading: ''
  footer-content: ''
  footer-includes-milestone: false # this is missing
  milestone-replace-text: ''
  include-sha-section: false # this is missing
  sha-section-heading: SHA256 Hashes of the release artifacts
  sha-section-line-format: '- `{1}      {0}`'
export:
  include-created-date-in-title: false # this as well
  created-date-string-format: ''
  perform-regex-removal: false # and this
  regex-text: ''
  multiline-regex: false # and yes, this one also
issue-labels-include:
- Bug
- Duplicate
- Enhancement
- Feature
- Help Wanted
- Improvement
- Invalid
- Question
- WontFix
issue-labels-exclude:
- Internal Refactoring
issue-labels-alias: []

Context

Forgot the configuration for the newly added sha section enabling (Don't judge 😄).

Other things

I believe I have found the cause (all C# default values are ignored), and think I have found a fix for this and a PR is coming soon.