[1pt] feedback: Data model | Add a sharded space example

[TarantoolBot]

Product: Tarantool
Audience/target: dev
Root document: https://www.tarantool.io/en/doc/latest/book/box/data_model/
SME: @ Totktonada

Details

The current example doesn't illustrate sharded spaces. It would be helpful if we reflected a sharding situation in the example. Check with the SME if we can replace the current example with the one below.

---

<…>describe a data schema
in the YAML format in a declarative way.
|The schema would look something like this|:
spaces:
users:
engine: memtx
is_local: false
<…>

https://www.tarantool.io/en/doc/latest/book/box/data_model/#data-schema-description-using-the-ddl-module

Create example for sharded space:

Something like this:

spaces:
    users:
      engine: memtx
      is_local: false
      temporary: false
      format:
      - {name: user_id, type: uuid, is_nullable: false}
      - {name: fullname, type: string,  is_nullable: false}
      - {name: bucket_id, type: unsigned, is_nullable: false}
      indexes:
      - name: user_id
        unique: true
        parts: [{path: user_id, type: uuid, is_nullable: false}]
        type: HASH
      - name: bucket_id
        unique: false
        parts: [{path: bucket_id, type: unsigned, is_nullable: false}]
        type: TREE
      sharding_key: [user_id]
      sharding_func: test_module.sharding_func