Bump version 4.0.0

[Marc-Andrieu]

Important

We really need to release new versions soon, as we have not for several months and there's some time needed to test in alpha before prod.

This goes hand in hand with the major version bump for Titan.

Both PRs are ready, and seemingly waiting for some more breaking changes to be merged, including (by likelihood):

• Allow students from other Schools to have a MyECL account: Schools #641
• MyECLPay: MyECLPay #611
• "Centrale Mega Meme" Meme module: [no PR yet] see branch
• External Notifications: Send notification content through Firebase and add an Arq scheduler #613

[Daihecyy]

Agreed only from a technical standpoint, consider thoroughly if such a bump is need