[Badge] add subtle variant

[DanielleRameau]

Add a border in the badge component. Right now there are some a11y issues regarding contrast.

### Tasks
- [ ] current badge will be called 'strong badges'
- [ ] add 'subtle badges' with a lighter background
- [ ] add variant in SL theme
- [ ] Copy to all themes (+ styling)
- [ ] add variant in code
- [ ] explain in documentation when to use strong or subtle badges
- [ ] update figma options table in  documentation