chore(utils): Provide a mikro orm base entity (#7286)

**What**
Provide a new mikro orm base entity in order to abstract away the on init and on create which include the id auto generation if not provided. The main goal is to reduce complexity in entity definition

.changeset/old-candles-cough.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/utils": patch
+---
+
+chore(utils): Provide a mikro orm base entity