[PREVIEW ONLY] Change default to SWDMv4

[fershad]

Triage

Type of change

Please select any of the below items that are appropriate.

This pull request:

• Adds a new carbon estimation model to CO2.js
• Adds new functionality to an existing model
• Fixes a bug with an existing model implementation
• Add other new functionality to CO2.js
• Add new data to CO2.js
• Improves developer experience for contributors
• Adds contributors to CO2.js
• Does something not specified above

Related issue/s

Please list below any issues this pull request is related to.

• Detail roadmap for changing to SWDM v4 as default #209

Docs changes required

Do any changes made in this pull request require parts of the CO2.js documentation to be updated?

• Yes
• No
• I don't know

A message will be added to the docs website to notify users of the upcoming change to v4 and the @next release they can use to test it. Further changes will be required when merging next into main.

Describe the changes made in this pull request

This change sets the default estimation model in CO2.js to Sustainable Web Design v4. It is currently for preview purposes only.