feat: init migrations for transactional tables (#9946)

# Which Problems Are Solved

To start with transactional tables we need to setup the new `zitadel`
schema in a way that does not rely on the event store later.

# How the Problems Are Solved

Setup step added which calls the function which executes the migrations.

# Additional Changes

none

# Additional Context

- closes #9933

backend/v3/storage/database/migration.go

@@ -0,0 +1,8 @@
+package database
+
+import "context"
+
+type Migrator interface {
+	// Migrate executes migrations to setup the database.
+	Migrate(ctx context.Context) error
+}