[OUDS] Docs: add 'Helpers > Clearfix' page

[vprothais]

Related issues

Listed in #2589.

Description

This PR adds the "Helpers > Clearfix" page based on:

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

Types of change

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

Live previews

• https://deploy-preview-2673--boosted.netlify.app/docs/0.0/helpers/clearfix/

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[julien-deramond]

Few comments. On top of that, we can uncomment the following line from the float.md file: <!--Use the [clearfix helper]({{< docsref "/helpers/clearfix" >}}) on a parent element to clear floats.-->.