Enable new Greenpeace visual identity

Summary

Release the new Greenpeace visual identity, applying all the changes done in PLANET-6945 Epic tickets.

Requirements

• Add a description text to the feature toggle to indicate its EOL date (eg. This opt-out setting will be phased out at the end of May)
• Manually enable the relevant feature toggle under Appearance > Customize > Site identity for all websites that don't have UI customization of their own.
• Post a notice on #p4-dev, especially for NROs where this won't be enabled by default, stating the EOL date so that NRO developers are informed.

Resources

• Sheet with child-theme customizations status (child-theme column).