hotfix(0.18.1): merge into develop

[seaerchin]

Problem

1. old sites that are on github but not on db are mistakenly returned as 404 as the db query is empty
2. DOMPurify too restrictive on BE

   Solution

3. check data on github in addition to checking sites.
4. use same setup as FE

[seaerchin]

Nits: we shouldnt have an additional call to github if the site already exists in our db. But since this is non-functional and more of an optimisation, we can tackle this after our hotfix!

yea but then it becomes q hard to read cos you have nested ifs