feat: implement user schema management (#7416)

This PR adds the functionality to manage user schemas through the new user schema service.
It includes the possibility to create a basic JSON schema and also provides a way on defining permissions (read, write) for owner and self context with an annotation.

Further annotations for OIDC claims and SAML attribute mappings will follow.

A guide on how to create a schema and assign permissions has been started. It will be extended though out the process of implementing the schema and users based on those.

Note:
This feature is in an early stage and therefore not enabled by default. To test it out, please enable the UserSchema feature flag on your instance / system though the feature service.

internal/repository/user/schema/aggregate.go

@@ -0,0 +1,25 @@
+package schema
+
+import (
+	"github.com/zitadel/zitadel/internal/eventstore"
+)
+
+const (
+	AggregateType    = "user_schema"
+	AggregateVersion = "v1"
+)
+
+type Aggregate struct {
+	eventstore.Aggregate
+}
+
+func NewAggregate(id, resourceOwner string) *Aggregate {
+	return &Aggregate{
+		Aggregate: eventstore.Aggregate{
+			Type:          AggregateType,
+			Version:       AggregateVersion,
+			ID:            id,
+			ResourceOwner: resourceOwner,
+		},
+	}
+}