Closes #772: Changed webp to avif and slight modification to UI

[Khadreal]

Description

Modified the settings page, changed title from webp to avif and checkbox option name

Fixes #772

Type of change

• New feature (non-breaking change which adds functionality).
• Enhancement (non-breaking change which improves an existing functionality).

Is the solution different from the one proposed during the grooming?

No

Checklists

Generic development checklist

• My code follows the style guidelines of this project, with adapted comments and without new warnings.
• The CI passes locally with my changes (including unit tests, integration tests, linter).
• If applicable, I have made corresponding changes to the documentation. Provide a link to the documentation.