Improve landing pages UI

[mayan-000]

Description

This PR adds code for updating the UI for the landing page with new content and styles.

Relevant Technical Choices

Testing Instructions

• Clone this branch and build the extension.
• Open PSAT panel and click on Site boundaries landing page.
• The page should open with 4 tiles showing new content.
• Click on any tile will open new page with docs related to the topic clicked.
• Try same Tracking protection and Private advertising landing pages.

Additional Information:

Screenshot/Screencast

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Checklist

• I have thoroughly tested this code to the best of my abilities.
• I have reviewed the code myself before requesting a review.
• This code is covered by unit tests to verify that it works as intended.
• The QA of this PR is done by a member of the QA team (to be checked by QA).

Fixes #

[gagan0123]

@mayan-000 @mohdsayed

Can we please use the UTM parameters, ?utm_source=psat&utm_medium=extension as added to other outbound links from the extension?

[gagan0123]

Ref: #506

[mohdsayed]

@mayan-000 @mohdsayed

Can we please use the UTM parameters, ?utm_source=psat&utm_medium=extension as added to other outbound links from the extension?

Done and pushed to develop

[gagan0123]

Thanks 👍