Add support for webarchive.org.uk

**Is your feature request related to a problem? Please describe.**

The add-on doesn't have the ability to check https://www.webarchive.org.uk for archives of websites
**Describe the solution you'd like**

Add webarchive.org.uk as an option to look for archived websites

**Describe alternatives you've considered**

**Additional context**

https://www.webarchive.org.uk is a website setup by the British Library to archive all websites in the UK