[Feature]: Add branch next in all repositories

### 🚀 Feature Proposal

Repositories need a new branch called `next`. This branch is important to exist, so we could work in the next release of the framework with a lot of breaking changes.

For example, right now, Athenna is on v4. The branch `next` would contain code for `v5`.

### Motivation

Better logistic for the framework implementation.

### Example

_No response_

Start by reviewing the AthennaIO repository organization and current branch and release workflow; the issue names no files, tests, or entry points. Confirm which repositories are in scope and verify that a `next` branch exists in each one for the planned v5 work.

Written by the indexing model from the issue text.