[enforced restrictions] add help html option; allow multiple claim_sources

config/example-config.yaml

go.mod

go.sum

internal/config/config.go

internal/endpoints/redirect/redirectEndpoint.go

internal/oidc/authcode/codeexchange.go

internal/oidc/authcode/enforced_restrictions.go

internal/oidc/userinfo/userinfo.go

internal/server/web/sites/error.mustache

internal/utils/ctxutils/errorpage.go