Don't hotlink the GitHub avatars

[ivan-aksamentov]

This is about the contributors portraits in the footer.

Currently we take image URls which all-contributors provide (generated automatically):
https://github.com/hodcroftlab/covariants/blob/master/.all-contributorsrc

The URLs are used here:

covariants/web/src/components/Common/TeamCreditsContributor.tsx

Line 57 in e412610

<Portrait src={contributor.avatar_url} />

We might either download the images as a build step and then serve them ourselves, or to use something like Next.js image component which will handle this automatically (if I remember correctly).