Add per-provider enrich with userinfo endpoint setting

[s3n-w6i]

What

This change introduces a checkbox into the provider settings that allows enabling the existing enrich_login_id_token_with_userinfo option on a per-provider basis.
To be backwards compatible, if the global enrich_login_id_token_with_userinfo is set to true, the userinfo endpoint is still fetched for all providers, regardless of their per-provider setting.

Why

• It depends on the provider whether the userinfo endpoint needs to be fetched, so a per-provider setting better represents that.
• For people with a hosted Nextcloud offering like myself, there may not be an option to set the global configuration option.

Open questions

• I have tested it successfully using a Keycloak instance. Are integration tests required?
• Regarding migration: This is a new option enrichLoginIdTokenWithUserinfo on the provider's settings object. This does not require any database schema changes, right?