Validate changelog changes in PRs

[dzinad]

Refs: https://github.com/mapbox/mapbox-navigation-android/pull/6072#issuecomment-1189493804

Now we have the changelog verification build that checks just the fact that CHANGELOG was updated. But with the current approach we can easily put the line in the wrong place if the PR was open, then there was a release, then the PR was merged. Suggested solution is to check not only that the file was updated, but also the following:

1. Added lines are in the Unreleased section;
2. Entries are not duplicated across multiple subsequent stable releases with incremental version (they can still be duplicated between pre-releases and stable releases).

Changelog verification happens here.

[dzinad]

BTW, looks like pr link check is not working: it just checks that there are PR links in the diff, while diff is sth like:

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d5960be9d68..4a5bd3d04af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@ Mapbox welcomes participation and contributions from everyone.
 
 ## Unreleased
 #### Features
+- Added ddtest.
 - Added `ViewBinderCustomization.infoPanelBinder` that allows installation of a custom info panel layout in `NavigationView`. [#6049](https://github.com/******/******-navigation-android/pull/6049) 
 - Added `ViewStyleCustomization.infoPanelPeekHeight` that allows customization of `NavigationView` info panel bottom sheet peek height. [#6049](https://github.com/******/******-navigation-android/pull/6049) 
 - Added `ViewStyleCustomization.infoPanelMarginStart`, `ViewStyleCustomization.infoPanelMarginEnd`, `ViewStyleCustomization.infoPanelBackground` that allows customization of a `NavigatioView` default info panel margins and background. [#6049](https://github.com/******/******-navigation-android/pull/6049)

So the check succeeds event though I did not add a link to the new line.