Stop accepting the id field for Collections on Collections creation

## 🎉 Description

Check the Collection router and stop accepting the `id` field from the front on the Collection creation. Instead, let the DB handle the id default creation using the `gen_random_uuid()` method.

Related: decentraland/builder-server#320

Start at the Collection router named in the issue and trace the creation input through to the database. Verify that a client-supplied id is no longer accepted and that creation leaves id generation to the database via gen_random_uuid(); confirm the resulting Collection still receives an id.

Written by the indexing model from the issue text.