Investigate lazysizes library to improve loading & image component

[gavinspence]

Is your feature request related to a problem? Please describe. The lazysizes library could help improve the lazy loading performance of our images and reduce unnecessary complexity in our image component by not having to calculate the image sizes attribute for every image.

Details can be found here:

• https://afarkas.github.io/lazysizes/index.html
• https://github.com/aFarkas/lazysizes/issues/545

Describe the solution you'd like

• [ ] Investigate benefits of the lazysizes library
• [ ] Understand potential performance improvements

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Testing notes [Tester to complete]

Dev insight: Will Cypress tests be required or are unit tests sufficient? Will there be any potential regression? etc

• [ ] This feature is expected to need manual testing.

Checklist

• [ ] (BBC contributors only) This issue follows the repository use guidelines

Additional context Add any other context or screenshots about the feature request here.