[vtctld] Migrate GetVSchema to VtctldServer

[ajm188]

Description

This PR addsGetVSchema to the VtctldServer API.

Example:

❯ vtctldclient --server "localhost:15999" GetVSchema commerce
{
  "sharded": false,
  "vindexes": {
  },
  "tables": {
    "corder": {
      "type": "",
      "column_vindexes": [
      ],
      "auto_increment": null,
      "columns": [
      ],
      "pinned": "",
      "column_list_authoritative": false
    },
    "customer": {
      "type": "",
      "column_vindexes": [
      ],
      "auto_increment": null,
      "columns": [
      ],
      "pinned": "",
      "column_list_authoritative": false
    },
    "product": {
      "type": "",
      "column_vindexes": [
      ],
      "auto_increment": null,
      "columns": [
      ],
      "pinned": "",
      "column_list_authoritative": false
    }
  },
  "require_explicit_routing": false
}

Related Issue(s)

• RFC: Vtctld Service #7058

Checklist

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

Deployment Notes

Impacted Areas in Vitess

Components that this PR will affect:

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

[rohit-nayak-ps]

lgtm