PopPUNK v2.6.3

Hotfix to fix some external cluster assigments #298
Also move docs to https://poppunk.bacpop.org/

What's Changed

• Update readthedocs config file to v2 by @johnlees in #291
• Add the roadmap to the docs by @johnlees in #292
• Add actions for docs build by @johnlees in #293
• Rename docs action by @johnlees in #294
• Use gha to publish docs by @johnlees in #295
• Remove permissions and add CNAME by @johnlees in #296
• Add permissions again by @johnlees in #297
• Poppunk assign fix by @samhorsfield96 in #298

Full Changelog: v2.6.2...v2.6.3