[Config] Update the 'Sharding with vshard' guide to using a new config

[andreyaksenov]

Related doc issues: https://github.com/tarantool/doc/issues?q=is%3Aissue+is%3Aopen+label%3A3.0%2C3.1+label%3Aconfig+label%3Avshard+

Product: Tarantool
Since: 3.0/3.1
Root document: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/
SME: @ Totktonada

Details

Note that some options are not implemented yet, so this guide should be updated when they are released (in v3.1 ???):

• Weights (zone):
  https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#replica-weights (not implemented yet)
• Replica set weights:
  https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#replica-set-weights (done in v3.1: sharding.weight)
• Rebalancer disbalance threshold: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#rebalancing-process (done in v3.0: sharding.rebalancer_disbalance_threshold)
• Parallel rebalancing: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#parallel-rebalancing (done in v3.0: sharding.rebalancer_max_sending, sharding.rebalancer_max_receiving)
• Replica set lock and bucket pin: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#replica-set-lock-and-bucket-pin (partially done in v3.0: sharding.lock, no pinned_count)
• Bucket ref: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#bucket-ref (doesn't affect the config)
• Defining spaces: https://www.tarantool.io/en/doc/latest/book/admin/vshard_admin/#defining-spaces (should we use box.once() now?)