feat(server): Add config option to disable admin registration

[provokateurin]

Description

Since it is possible to create Immich admin users via OIDC, registering an admin user first is no longer a strict requirement. Therefore an option (default disabled) is needed to skip this step.

Fixes #18847

How Has This Been Tested?

• Setup a fresh instance with OIDC config. Open the web page, get redirect to the OIDC provider instead of having to register an admin user first.

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

None, all written by hand.

[danieldietzler]

Thanks!

[immich-push-o-matic]

📖 Documentation deployed to docs.pr-24539.preview.immich.app

[jrasm91]

You need to expose this in the API, by updating SystemConfigOAuthDto. You should also add this option as a switch/toggle in the web ui.

[provokateurin]

Ok, I'll have a look!

[provokateurin]

I added a switch, but while trying to confirm that it works i realized that it is pretty useless. You can only see the settings page if you have already registered an admin user and are logged in as this user. So this config option does not make sense if you don't use the config.json file. Also disabling after already having created an admin user will have no effect.

@jrasm91 what do you think?

[jrasm91]

Oh, true. Probably we don't need the switch in the UI, since it's useless in this case. I think we should probably still add it to the dto though, since that is used for validation. I'm actually surprised that the functionality would work without validation. How is it loading the value from the config file if wasn't added to the dto?

[provokateurin]

Isn't the Dto only used for API stuff? As far as I could tell it's not really used in this case, as the config value is only used on the server.