[component]: Footer

[Cian77]

Description

Open issues:

Design:

• [x] Integrated new typography
• [ ] Design review 20. Sept. 20
• [ ] Spacing is defined
• [ ] Documentation final

Tokens:

• [ ] Typography tokens ready

Design

https://www.figma.com/design/JIT5AdGYqv6bDRpfBPV8XR/Foundations-%26-Components-Next-Level?node-id=558-7013

Tokens

• [ ] Tokens for this component are ready

Requirements

• On mobile, the link lists should be wrapped by an accordion
• Almost all elements are optional, the only required elements are the imprint/accessibility links and the copyright information
• It should be easy to compose the footer with custom data, there should not be a different component structure for mobile and desktop (for developers), the accordion wrapping should happen internally
• Aria requirements have to be met, link lists need to be connected to their heading via aria-labelledby. If the heading is not visible, aria-label can be used as well (see https://www.figma.com/design/p5pBgXMdRs9eM2HzzeXh4z/Menus?node-id=2-7158&t=Mam0iMG60hAkbUrx-1 for more details)
• Heading levels should be configurable

Tasks

### 💻 Tasks
- [ ] https://github.com/swisspost/design-system/issues/3457
- [ ] https://github.com/swisspost/design-system/issues/3458
- [x] Review Design (All states present? Possible to implement?)
- [ ] HTML/CSS component implementation
- [ ] Documentation in Storybook
- [ ] Unit tests
- [ ] End to end tests
- [ ] Visual regression tests
- [ ] Design review