[sso/oidc] Implement OIDC client in iam component

[AlexTugarev]

part of Epic: Single sign-on (SSO) #7761

• Should use OIDC Client Configs from DB

  • a simple workaround to decouple the efforts would be to read them from configmap first

• Underlying libraries, e.g. the actual protocol mechanics are the following. (that's a different view on the dependency question, as the all-in-one projects like oauth2-proxy come with drawbacks w.r.t configuration needs.)

  • https://github.com/coreos/go-oidc (8yo), mature, but not certified and client-only
  • https://github.com/zitadel/oidc (3yo), newcomer, but certified and client+server

[AlexTugarev]

If #15727 is merged, we can spawn follow-up issues to fix/implement the remaining of this.