Add drush release-notes / rn command

[jenlampton]

Maintainers often use the drush release-notes command to generate a list of changes since the last release of their project:
https://drushcommands.com/drush-8x/grn/release-notes/

I would love to have this command in bee :)

[indigoxela]

@jenlampton are you aware that you can simply do that via GitHub UI or API?

So far I never used that command, wasn't even aware of it, and wouldn't use it if it existed.

And also: this command would only be useful for a minority of Bee users (some maintainers), so I don't think this belongs in Bee core.

[Wylbur]

I tried to run this in a Drupal 7 site with Drush 8.4.11, and I got 'command not found'. Could this have been dropped at some point?

[yorkshire-pudding]

I tried to run this in a Drupal 7 site with Drush 8.4.11, and I got 'command not found'. Could this have been dropped at some point?

@Wylbur - looking at the link provided, it seems this was written for Backdrop. see backdrop-drush-extension/grn though it is based on a Drupal add-on module for drush - https://www.drupal.org/project/grn

@jenlampton - can I ask what the use case for this, given github also does this and populates it right in the release box ready for editing? I can't see any benefit to doing this on the command line.