ci(*:skip) Improve automated changelog generation

[charlesbvll]

Issue

Description

Our changelog generation script didn't work automatically with our new PR title format.

Related issues/PRs

N/A

Proposal

Explanation

Use the PR title to categorise the PRs.

Checklist

• [x] Implement proposed change
• [x] Make CI checks pass
• [x] Ping maintainers on Slack (channel #contributions)

Any other comments?

N/A

[charlesbvll]

Instead of moving update_changelog to dev, it would be better to keep it in flwr_tool and eventually move flwr_tool into a separate project

Shouldn't this be done in a separate PR? I feel like in terms of consistency, it makes more sense to have everything under dev/ (as flwr_tool currently only contains the protoc.py script, whereas dev/ contains all dev scripts similar to the update_changelog.py script)

[danieljanes]

The "move flwr_tool into a new project" should happen separately. But we had update_changelog.py in flwr_tool already (this PR removes it), so I'd recommend to leave it there and make the changes in the version in flwr_tool.

[charlesbvll]

The "move flwr_tool into a new project" should happen separately. But we had update_changelog.py in flwr_tool already (this PR removes it), so I'd recommend to leave it there and make the changes in the version in flwr_tool.

@danieljanes But this new script uses the same changelog_config.toml file as does check_pr_title script. This is why it was moved to dev/ so we don't have to do some relative path handling