Improve Settings page headings

[georgewrmarshall]

Description

There is currently some inconsistency with the headings on the settings page that I noticed when reviewing the SRP quiz. Semantic HTML could also be greatly improved.

https://github.com/MetaMask/metamask-extension/assets/8112138/4ea46233-c7ec-4021-b231-5feb071443ec

Technical Details

• Improve the styling and the sematic html of the settings page
• Update "Settings" to <Text variant={TextVariant.displayLg} as="h1">
• Update "General", "Advanced", "Contacts", "Security & privacy", "Alerts", "Networks", "Experimental", "About" to be to use <Text variant={TextVariant.displayLg} as="h2">

Acceptance Criteria

• heading styles are consistent and show visual priority on all settings pages
• html headings are in order e.g. h1, h2, h3 etc

[ayushj1910]

Hey @georgewrmarshall , I would like to work on this task.