Allow blank sections under the unreleased section

[h-artzi]

Is your feature request related to a problem? Please describe.

Can't add blank sections under the unreleased section of the changelog.

A clear and concise description of what the problem is. Ex.I would like to see [...] because [...].
Please include the intended use case and what the feature would improve on so that we can prioritize
the feature accordingly.

We would like to add the following sections under the Unreleased section of a changelog after a version release.

### Added
### Changed
### Deprecated
### Removed
### Fixed
### Security

This would ensure that developers are aware of all the possible sections they can add to while updating the Changelog.
Then when we cut the next release, we would be in charge of removing the unused sections.

Describe the solution you would like

Allow the use of blank sections in the Unreleased section as long as they are part of the following set (added, changed, deprecated, removed, fixed, security)

Describe alternatives you have considered

• Not having this in the changelog, and developers potentially misplacing entries.
• The use of a dummy entry such as This is a dummy entry

Additional context