fix(a11y): better a11y on doc

[louismaximepiton]

Related issues

NA

Description

Add some unique roles that might be an issue in the future to better convey information to ATs.

Checklists

• I have read the contributing guidelines
• My change follows the developer guide
• My change follows the page structure defined in [OUDS] Create a component page template for the doc #3045
• Title and DOM structure is correct
• Links have been updated (title change impacts links for example)

Progression (for Core Team only)

• Code review
• Commit on ouds/main following conventional commit

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[MaxLardenois]

I have questions about the roles on footer and banner

[MaxLardenois]

<header> element has a banner role by default (except if it is inside another semantic element, but it's not the case here)

[louismaximepiton]

It's mainly in prevention, for people using old ATs/browsers couples and don't support this by default (which happens a lot on the few figures I have, but they may be wrong by the time (https://access42.net/uploads/2017/06/presentation_etude-le-bv_05122017v2.pdf) (2020 figures haven't been published yet and I don't know why 🤷)).

It's only proposals, but we can remove the PRs since these changes should be only for the old couples.

[vprothais]

The document is very old, more than 8 years old, not sure if it is still relevant. I would probably remove it, if it is already the built-in role.