Document Snaps dialogs and home pages

[alexandratran]

Description

Add feature pages under Custom UI for Snaps dialogs and home pages. Include screenshots, examples.

Clean up and make minor edits to related content for consistency, accuracy, and simplicity.

Issue(s) fixed

Fixes #1267 Fixes #1268

Preview

• https://docs.metamask.io/1267-snaps-dialogs/snaps/features/custom-ui/dialogs/
• https://docs.metamask.io/1267-snaps-dialogs/snaps/features/custom-ui/home-pages/

Checklist

Complete this checklist before merging your PR:

• [x] If this PR contains a major change to the documentation content, I have added an entry to the top of the "What's new?" page.
• [x] The proposed changes have been reviewed and approved by a member of the documentation team.

[github-actions[bot]]

Preview published: 1267-snaps-dialogs

[github-actions[bot]]

Preview published: 1267-snaps-dialogs