Add version and compare links to the api changelog generator

What does this MR do and why?

Extend the Gitlab::Changelog::Release that now also adds two link:

• Check files: Link to the tree site of the to position of the release
• Compare commits: Link to the compare site between from and to of the release from and to will be provided by Repositories::ChangelogService when calling the api.

This allows a fast way to review the changed code from release that is mentioned in the changelog. The manually opening of the compare site and search for the tags can be skipped. Since relative refs like Branches and HEAD are allowed for from and to parameter we will internally substitute them to the commit id. TODO: Preserve Git Tags when used.

Notes

• I currently could not find a way to use GitLab-specific references for this kind of wanted links. Instead there will be added absolute links for this.
• Markdown compare only works with commit ids but the compare itself also works with tags.
• There is also currently no multi language support for the links labels. See !72007 (comment 801320946)

Screenshots

Before	After

How to set up and validate locally

• Apply Changes form the MR to your GitLab Instance
• Restart GitLab Instance

  gitlab-ctl restart

• Create a API Key (eg. Project Access Token) with api write access to your gitlab project. Needed to trigger the changelog creation later.
• Inside your Project navigate to Setting => Gerneral to find your needed Project ID
• Follow Workflow inside our existing Git Project from the patched GitLab Instance to create the Changelog via the API:
  • Note: You need to replace <project id> and <token> with your settings from the last steps.

  git tag v1.0.0
  touch test.md
  git add test.md
  git commit -m "test change
  
  This is just a test Change
  
  Changelog: other"
  git push --tags origin master
  curl --header "PRIVATE-TOKEN: <token>" --data "version=1.0.1" "https://gitlab.com/api/v4/projects/<project id>/repository/changelog"
  git pull
  git tag v1.0.1
  git push --tags origin master

Related issues

Closes #348221

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