Add authCodeOptions to openidConnect Provider

[JensHeise]

This pull request enables the possibility to add custom URL params to the authentication URL.
It can be used as follows:

openidConnect, err := openidConnect.New(clientId, clientSecret, callBackUri, discoveryUri, "openid", "profile", "email", "offline_access")
if err != nil {
	slog.Error("Error creating openidConnect provider: ", "err", err.Error())
}
openidConnect.SetAuthCodeOptions(map[string]string{
	"domain_hint": "yourdomain.com",
})

Use cases for the URL params are e.g. domain hints or prompt configuration.