[lead text]: Add styles for the lead text component

[oliverschuerch]

Description

Implement lead text styles

Design

• [x] Integrated new typography
• [ ] Spacing is defined
• [ ] Documentation final

Design

https://www.figma.com/design/JIT5AdGYqv6bDRpfBPV8XR/Foundations-%26-Components-Next-Level?node-id=178-6713&node-type=frame&t=X3tyO53unPAPaH3B-0

Tokens

• [x] Tokens for this component are ready

DEVs proposal

Base styles: body Token set name: Components/Lead

• post-lead-font-size (D 24, T 20, M 18)
• post-lead-font-weight (700 or bold)

Tasks

### 💻 Tasks
- [ ] Review Design (All states present? Possible to implement?)
- [ ] https://github.com/swisspost/design-system/issues/3496
- [x] Remove all unused scss variables for this element
- [x] HTML/CSS implementation
- [x] Documentation in Storybook
- [ ] Design review

[Vandapanda]

Tokens implemented, ready for Devs