[OIDC] Config inheritance for multi-tenancy OIDC

[canidae]

Some configuration duplication may be avoided for multi-tenacy OIDC if configuration options were inherited from the default OIDC config.
If configuration is not to be inherited, a better error message should be given to the user upon missing configuration values for a tenant. Currently it will only say for example Both 'auth-server-url' and 'client-id' or alternatively 'public-key' must be configured when the quarkus-oidc extension is enabled, but it doesn't say which tenant is missing these values.

This issue was raised after a discussion here: #12254