Fix dev:oidc npm script

[alxndrsn]

• generate public/client-config.js at foreman startup
• remove nginx's special handling for client-config.js

Closes #1034

[matthew-white]

I'm interested in what you think of #1038, but this approach also looks reasonable to me. It'd be nice to remove the addition of Docker in the Procfile though, since that's being discussed at #1035.

remove nginx's special handling for client-config.js

We have special logic around this file in prod as well, so my feeling is that it's OK to have some special handling in this local nginx config. But I also don't have any attachment to it: I'd be OK generating client-config.json locally, as this PR does, if you think that's the best approach.

[alxndrsn]

#1034 not recreatable, so this change is not required.