fix: remove enforced headline styling and update migration guide

[mariohamann]

Description:

This is fixing what was commented in this PR but was neither there addressed nor in this PR.

Definition of Reviewable:

• Documentation is created/updated
• Migration Guide is created/updated

• E2E tests (features, a11y, bug fixes) are created/updated

• Stories (features, a11y) are created/updated
• relevant tickets are linked

[changeset-bot]

⚠️ No Changeset found

Latest commit: 6246013

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[github-actions]

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[auroraVasconcelos]

Approved with the assumption that it doesn't need a changeset as it would repeat the one from #3165