vshard: vshard.router.buckets_info shows name

[TarantoolBot]

Related dev. issue: tarantool/vshard#426
Related doc. issues: #3942, #3944

Product: Tarantool, vshard
Since: 3.0, 0.1.25
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_rock/vshard/vshard_router/
SME: @ Totktonada, @ Serpentian

Details

When identification_mode is name_as_key, buckets_info()
also returns name of the replicas, where buckets are stored:

tarantool> vshard.router.buckets_info()
---
- - uuid: aaaaaaaa-0000-4000-a000-000000000000
    status: available_rw
    name: replica_1_a

Requested by @Serpentian in tarantool/vshard@daa31a0.