Web: Setup dedicated IndieAuth provider or implement IndieAuth client

[m-i-l]

The site is currently using https://indielogin.com/ as its IndieAuth provider. As per discussion with aaronpk (see https://chat.indieweb.org/dev/2020-07-12) "i don't want too many people to rely on indielogin.com itself, i would rather they implement an indieauth client directly or set up an instance of indielogin.com for themselves".

Need to work out the best way of doing this. Either it could be a fork of https://github.com/aaronpk/indielogin.com hosted in its own container at e.g. indielogin.searchmysite.net, or the indieauth client code could be directly integrated into src/wec/content/dynamic/searchmysite/admin/auth.py.

See also https://indieauth.net/ for more information on IndieAuth.