Organize Image Optimization options: Add f_avif support & recommend f_auto

[gabrielcld2]

Approach

Improve the image optimization setting options:

• Add the AVIF option within the dropdown which will set the value to f_avif
• Rename the label for the f_auto option to read as Auto (Recommended)

QA notes

• Go to the Image Settings page
  • Set the Image Format to Auto (Recommended)
  • Save the changes
• On a post/page:
  • add a new image
  • save the changes and view the page on the frontend
  • make sure the image is being served using the f_auto format option
• Repeat the steps above but this time by setting the Image Format to AVIF