Footer prop `footer` not in use

### Purpose

- [ ] New feature
- [ ] New renderer
- [x] Bug fix
- [ ] Documentation
- [ ] Refactoring
- [ ] Test Case
- [ ] Other

### Description

The Footer Block does not use the `footer` prop.

### Possible solution

Use the `footer` prop, if provided. To maintain compatibility, if not provided, pass `header` as it is nowadays.
