Add time-converter extension

[alexj]

Description

Screencast

Checklist

• [x] I read the extension guidelines
• [x] I read the documentation about publishing
• [x] I ran npm run build and tested this distribution build in Raycast
• [x] I checked that files in the assets folder are used by the extension itself
• [x] I checked that assets used by the README are placed outside of the metadata folder