Fix changelog parsing on ignored packages (when PRs are either labeled or unlabeled)

[NullVoxPopuli]

Resolves: embroider-build/create-release-plan-setup#91

Helps with: adopted-ember-addons/program-guidelines#28

Unblocks: NullVoxPopuli/limber#1673
As well as a few releases on the adopted ember addons org (I don't remember where now, but folks have arbitrarily been working around the problem by adding internal to their PRs -- so this is more a fix for a big annoyance than a fix for something show-stopping).

This seems to do what I want, however it looks like like we need to do further changelog filtering and not use @ef4/lerna-changelog's default output.

• package list should exclude private packages
• package groups should be combined since if just removing the string, we'd have duplicate package groups.

Alternate fix here: embroider-build/github-changelog#16 (which I think is he correct fix and we should not merge this (#60) PR)

Testing

In the root package.json:

"release-plan": "github:embroider-build/release-plan#dist/ignore-private-packages-detected-from-the-changelog-generator-dist"

or

"release-plan": "github:embroider-build/release-plan#bbd8d70"

Preview: NullVoxPopuli/limber#1673

[mansona]

I agree that the github-changelog fix is the right fix so let's put our effort over there to make it happen 👍