docs(CHANGELOG): make changelog keepachangelog compliant

[mdevolde]

docs(CHANGELOG): make changelog keepachangelog compliant

Why the pull request was made

To have a changelog that is keepachangelog compliant, allowing users to follow the changes that are implemented since latest release.

Summary of changes

• Edit the changelog to follow keepachangelog conventions.
• Add an Unreleased section.
• Split releases in sub-sections.
• Make releases titles cliquable.
• Add a short introduction and edit the title.
• Edit pull request template to ask to edit changelog in PRs (and to add a change category "chore").
• Edit contributing file to ask to edit changelog in PRs.

Screenshots (if appropriate):

Not applicable.

How has this been tested?

Not applicable.

Resources

https://keepachangelog.com/en/2.0.0/

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update (changes to documentation only)
• Refactor / code style update (non-breaking change that improves code structure or readability)
• Tests / CI improvement (adding or updating tests or CI configuration only)
• Other (please describe):

Checklist

• Followed the project's contributing guidelines.
• Updated any relevant tests.
• Updated any relevant documentation.
• Added comments to your code where necessary.
• Formatted your code, run the linters, checked types and tests.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.46%. Comparing base (27493eb) to head (8b1c2c4).
⚠️ Report is 1 commits behind head on master.
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #199   +/-   ##
=======================================
  Coverage   80.46%   80.46%           
=======================================
  Files          13       13           
  Lines        1746     1746           
=======================================
  Hits         1405     1405           
  Misses        341      341           

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