ci: extract changelog for GitHub release notes

[Conaclos]

Summary

This PR updates the release workflows.
GitHub Release notes are now generated from the changelog.
The script extract the first subsection that starts with a digit, e.g. ## 1.1.0. This allows to skip ## Unreleased.

The changelog should be updated before every release.

I also removed useless fetch-depth parameter that is set to 1 by default.

Test Plan

Next release.

[ematipico]

Next release.

Isn't there another way to test it? Even locally, to show us what the script will generate

[ematipico]

It's best to create a bash script somewhere in the repository, maybe under a scripts/ folder. So we have one script used by all the workflows. If there's a bug, we would need to fix all the workflows and we might forget

[Conaclos]

I improved the script by using the Unreleased section if a section for the released version is not found. This allows supporting nightly releases.

Isn't there another way to test it? Even locally, to show us what the script will generate

I tested the script locally. However, there is no way to easily test the workflow...

[ematipico]

Even a local test is enough :)