[vtctld] Migrate GetSrvKeyspace as GetSrvKeyspaces in VtctldServer

[ajm188]

Description

This PR migrates the GetSrvKeyspace command and rpc to the newer VtctldServer, renamed as GetSrvKeyspaces. Changes:

• Support multiple cells at once.
• Return a mapping of cell => srvkeyspace, rather than a single srvkeyspace
• Support specifying no cells at all, in which case we look up all cells in the topo on behalf of the caller and return a full mapping.

Related Issue(s)

• Closes Migrate GetSrvKeyspace to VtctldServer #7679

Checklist

• Should this PR be backported? No
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

Example usage:

❯ vtctldclient --server "localhost:15999" GetSrvKeyspaces commerce zone1
{
  "zone1": {
    "partitions": [
      {
        "served_type": 1,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      },
      {
        "served_type": 2,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      },
      {
        "served_type": 3,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      }
    ]
  }
}
❯ vtctldclient --server "localhost:15999" GetSrvKeyspaces commerce zone2
{
  "zone2": null
}
❯ vtctldclient --server "localhost:15999" GetSrvKeyspaces commerce
{
  "zone1": {
    "partitions": [
      {
        "served_type": 1,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      },
      {
        "served_type": 2,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      },
      {
        "served_type": 3,
        "shard_references": [
          {
            "name": "0"
          }
        ]
      }
    ]
  }
}
❯ vtctldclient --server "localhost:15999" GetSrvKeyspaces -h
Usage:
   GetSrvKeyspaces <keyspace> [<cell> ...] [flags]

Flags:
  -h, --help   help for GetSrvKeyspaces

Global Flags:

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build/CI
• VTAdmin

[doeg]

Thanks!!! 🌻

[ajm188]

Latest commit reimplementing the legacy command using the new implementation:

Before

❯ vtctlclient -server "localhost:15999" GetSrvKeyspace zone1 commerce
{
  "partitions": [
    {
      "served_type": 1,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    },
    {
      "served_type": 2,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    },
    {
      "served_type": 3,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    }
  ],
  "sharding_column_name": "",
  "sharding_column_type": 0,
  "served_from": [
  ]
}

After

❯ vtctlclient -server "localhost:15999" GetSrvKeyspace zone1 commerce
{
  "partitions": [
    {
      "served_type": 1,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    },
    {
      "served_type": 2,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    },
    {
      "served_type": 3,
      "shard_references": [
        {
          "name": "0",
          "key_range": null
        }
      ],
      "shard_tablet_controls": [
      ]
    }
  ],
  "sharding_column_name": "",
  "sharding_column_type": 0,
  "served_from": [
  ]
}

[doeg]

Love to reimplement a legacy command using a new implementation. Still looks good to me!

@deepthi @rohit-nayak-ps would you mind looking at this one too, when you get a chance? :D

[deepthi]

Nice work! You always do such a nice job with comments and unit tests 💯