Add page margins option in the webtoon mode

[titan-19]

Describe your suggested feature

I'm simply talking about this option that exists in the suwayomi reader :

Other details

No response

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• [X] I have written a short but informative title.
• [X] I have updated the app to the latest version.
• [X] I will fill out all of the requested information in this form.