Keycloak 24.x User Profile default config + newly required user fields

[adrhine]

My team has been evaluating how 24.x will affect us and one thing that has come up is how the firstName and lastName attributes will be required by default for all users. For our existing realm this will definitely give us some trouble as we have customized many of the templates that are presented to the users, so they would be broken after the rollout. Naturally we would need to disable the requirement of these fields after the rollout of 24x, but during the rollout we don't want to serve any downtime for our users (those who are logging in or registering).

We've discussed some custom workarounds on our side that we could do to either seed the KC database or include some custom code that would overwrite the default config shipped in Keycloak, but we were wondering if this issue was one that other users of Keycloak would encounter as well - perhaps a solution in the Keycloak codebase would be preferable.

Some options could be

1. simply remove the required nature of firstName and lastName from the default config
2. the same as above, but only for existing realms
3. rather than having always using the hard-coded file keycloak-default-user-profile.json, Keycloak could offer a way to direct to another file

I'm sure there are other options that would be valid as well. We are trying to limit the amount of custom code that we are rolling out to support Keycloak (especially when it's just to support a one-time operation such as the rollout of 24.x). Would be interested in hearing the thoughts of anyone else running Keycloak as well on this.

I"d be happy to submit a PR for a modification if I could be advised on a most preferable solution here.

Related: #26489

[adrhine]

The related #26489 satisfies this for us. Thanks!