Add flag to omit empty sections from getChangelog task.

[ChrisCarini]

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

Similar to https://github.com/JetBrains/intellij-platform-plugin-template/blob/main/.github/workflows/build.yml#L166 , several of my OSS plugins also create a draft release using the getChangelog output. Every time I do a release, I have to edit the description and delete empty sections to keep the release notes (and changelog) short and simple. I'd rather have this automated, so that when the PR is opened, the empty sections are already removed - because I, along with many others, leverage this gradle plugin, I would like to pass a flag to this task to tell it to omit empty changelogs.

Describe the solution you'd like

A flag, such as --no-empty-secions, to omit empty sections from the output of getChangelog task.

Describe alternatives you've considered

awk, but it's ugly (there is probably a better, more concise way; this is what I ended up w/ after 30 min of googling):

./gradlew getChangelog --unreleased --no-header --console=plain -q  | awk 'function flush_print_maybe() {
                      if (matching > 2) printf("%s\n", buf)
                      buf = ""
                  }
                  /###/ { flush_print_maybe(); matching = 1 }
                  /^$/  { flush_print_maybe(); matching = 0 }
                  /.+/  { matching++ }
                  matching { buf = (buf == "" ? $0 : buf ORS $0) }
                  END   { flush_print_maybe() }'

Additional context

┌─(ChrisCarini)──(2023-04-29 @ 22:50:16)──( ~/GitHub/jetbrains/plugins/sample-intellij-plugin  (main) ) 
└─$ > ./gradlew getChangelog --unreleased --no-header --no-links --no-empty-sections --console=plain -q 
### Changed
- Upgrading IntelliJ from 2023.1 to 2023.1.1

### Deprecated
- Deprecated line


┌─(ChrisCarini)──(2023-04-29 @ 22:50:19)──( ~/GitHub/jetbrains/plugins/sample-intellij-plugin  (main) ) 
└─$ >

...vs...

┌─(ChrisCarini)──(2023-04-29 @ 22:50:19)──( ~/GitHub/jetbrains/plugins/sample-intellij-plugin  (main) ) 
└─$ > ./gradlew getChangelog --unreleased --no-header --no-links --console=plain -q 
### Added

### Changed
- Upgrading IntelliJ from 2023.1 to 2023.1.1

### Deprecated
- Deprecated line

### Removed

### Fixed

### Security


┌─(ChrisCarini)──(2023-04-29 @ 22:50:28)──( ~/GitHub/jetbrains/plugins/sample-intellij-plugin  (main) ) 
└─$ >