Mock OIDC identity provider

Registered on dev/preview Supabase branches as custom OIDC providers. Nothing here is a real identity.

client_id june-mock-idp-dev
custom:mock-google
issuer  https://idp.dev.junehealth.care/mock-google
discovery https://idp.dev.junehealth.care/mock-google/.well-known/openid-configuration
custom:mock-facebook
issuer  https://idp.dev.junehealth.care/mock-facebook
discovery https://idp.dev.junehealth.care/mock-facebook/.well-known/openid-configuration
custom:mock-apple
issuer  https://idp.dev.junehealth.care/mock-apple
discovery https://idp.dev.junehealth.care/mock-apple/.well-known/openid-configuration