[OUDS] Docs: add 'Helpers > Stretched link' page

[louismaximepiton]

Related issues

Listed in #2589.

Description

This PR adds the "Helpers > Stretched link" page based on:

• the previous corresponding Boosted page (see code source)
• the corresponding Bootstrap page (see code source)

To add to #2589

• Uncomment elements whenever /components/card is added
• Uncomment elements whenever /components/buttons is added
• Uncomment elements whenever /layout/grid is added
• Uncomment elements whenever /utilities/spacings is added

Types of change

• New documentation (non-breaking change which adds functionality)

Live previews

• https://deploy-preview-2719--boosted.netlify.app/docs/0.0/helpers/stretched-link

[netlify]

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[julien-deramond]

LGTM.
I modified tiny details to re-use what's in Bootstrap via c46b7bc.