Add a project schema version system

[Artusamak]

If a developer wants to require some new variables / settings for the project, there is no mechanism to guarantee that the whole team added the variable. It may lead to setup variations in the projects for the same environment.
One way to address that could be to set a new variable called COMABAWA_PROJECT_SCHEMA_VERSION for instance that would be checked by Combawa to require that the .env value of this variable match the value from settings.sh.
Eg: The system is installed once with the schema 101. Every developer setup its instance with the 101 version of the schema. Then a new schema version is required, the developer introducing the change bumps the schema version to 102. The team pulls the modifications, tries to build. Kaboom, they must update their .env value to 102 and apply the changes documented in the README in order to by able to build again.

I'm wondering if we would need to add a message when bumping the schema version to justify the update and document the changes to do. The README file should mitigate that, it should be updated when introducing a new change to have a documentation up to date, a new entry for the schema update could also be added and could contain the actions to do when switching to this version.

[Artusamak]

Duplicated by #11 ? =)

[DuaelFr]

We are not sure that this would be widely used so let's keep that in mind and rediscuss in the future.

[Artusamak]

https://github.com/jevakallio/git-notify could help.

[Artusamak]

As a more native and elegant solution, Symfony flex recipes may be something we could use for that. They are a schema versioned tool.

Can we specialize them per project easily? Host them privately?

[Artusamak]

https://symfony.com/doc/current/setup/flex_private_recipes.html

[Artusamak]

If we are lazy enough, Drupal might support it natively without having to do any extra effort.