Generate changelog from PR description

[AurelienFT]

The changelog is currently done manually in the codebase, however this creates a lot of conflicts that make loose time of developers (and reviewers that need to re-review after conflicts resolution).

In order to avoid this conflicts a solution could be to generate the changelog based on the PR description that will be formatted correctly. This generation could be done in all release branch.

Any other solution is welcomed (especially if it's an already existing free service and easy to deploy that will avoid us making the CI stuff)