Specify contributing rules and release workflow

[Purexo]

Main branch get major change.
Release/vx as release branch
Last release branch as default branch

All release commits should be merged in main

bugfix/vx-bugfix-name
feature/vx-feature-name

squash-merge for easy cherrypick a fix from a release to another releases if adaptés

Follow a git message format for be able to generate changelog

Tag each release
Github action on tag to build ans deploy package in gh packages registry

[Purexo]

https://www.conventionalcommits.org/en/v1.0.0/