feat: option to disallow public org registration (#6917)

* feat: return 404 or 409 if org reg disallowed

* fix: system limit permissions

* feat: add iam limits api

* feat: disallow public org registrations on default instance

* add integration test

* test: integration

* fix test

* docs: describe public org registrations

* avoid updating docs deps

* fix system limits integration test

* silence integration tests

* fix linting

* ignore strange linter complaints

* review

* improve reset properties naming

* redefine the api

* use restrictions aggregate

* test query

* simplify and test projection

* test commands

* fix unit tests

* move integration test

* support restrictions on default instance

* also test GetRestrictions

* self review

* lint

* abstract away resource owner

* fix tests

* lint

docs/docs/guides/manage/customize/restrictions.md

@@ -0,0 +1,14 @@
+---
+title: Feature Restrictions
+---
+
+New self-hosted and [ZITADEL Cloud instances](https://zitadel.com/signin) are unrestricted by default.
+Self-hosters can change this default using the DefaultInstance.Restrictions configuration section.
+Users with the role IAM_OWNER can change the restrictions of their instance using the [Feature Restrictions Admin API](/category/apis/resources/admin/feature-restrictions).
+Currently, the following restrictions are available:
+
+- *Disallow public organization registrations* - If restricted, only users with the role IAM_OWNERS can create new organizations. The endpoint */ui/login/register/org* returns HTTP status 404 on GET requests, and 409 on POST requests.
+- *[Coming soon](https://github.com/zitadel/zitadel/issues/6250): AllowedLanguages*
+
+Feature restrictions for an instance are intended to be configured by a user that is managed within that instance.
+However, if you are self-hosting and need to control your virtual instances usage, [read about the APIs for limits and quotas](/self-hosting/manage/usage_control) that are intended to be used by system users.

docs/sidebars.js

@@ -94,6 +94,7 @@ module.exports = {
             "guides/manage/customize/branding",
             "guides/manage/customize/texts",
             "guides/manage/customize/behavior",
+            "guides/manage/customize/restrictions",
           ],
         },
         {