fix(typography): modify .lead values to match the DSM body text

[julien-deramond]

Description

This PR fixes the .lead values (font-size, line-height and letter-spacing) for this class to match the body text definition in the DSM's design token (ods.web.sys.font.body.m).

This is needed for projects willing to have a less condensed rendering for articles for instance.

They are the following:

Size	font-size	line-height	letter-spacing
Desktop	20px	1.5=30px	-0.40px
Tablet	18px	1.5=27px	-0.20px
Mobile	16px	1.5=24px	-0.10px

The review must double-check these 3 values for each size: desktop, mobile and tablet.

Types of change

• Bug fix (non-breaking which fixes an issue)

Live previews

• https://deploy-preview-2363--boosted.netlify.app/docs/5.3/content/typography/#lead
• https://deploy-preview-2363--boosted.netlify.app/docs/5.3/migration/#contents

Checklist

Contribution

• I have read the contributing guidelines

Design

• My change respects the design guidelines defined in Orange Design System
• My change is compatible with a responsive display

Checklist (for Core Team only)

• My change introduces changes to the migration guide

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