Update yaml preview design on policy editor

What does this MR do and why?

Update yaml preview design on policy editor

• with Update policy-editor-layout to include rule mode (!90099 - merged) I mistakenly added some spacing in the pre value
• clean up borders
• add back white background

Changelog: changed

EE: true

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to a project => Security & Compliance => Policies => New policy => Scan Result Policy

MR acceptance checklist

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