[vtctldserver] Add additional backup info fields

[ajm188]

Description

This PR adds the following additional fields to the BackupInfo proto message:

• Keyspace => set by VtctldServer
• Shard => set by VtctldServer
• Time => the time the backup started, parsed out of the backuphandle name, set by BackupHandleToProto
• TabletAlias => the alias of the tablet that took the backup, parsed out of the backuphandle name, set by BackupHandleToProto
• Engine => the name of the backupstorage engine that produced the backup, currently unset, to be added in a future PR
• Status => the status of the backup, to be set by a combination of the backupengine implementation and the backupstorage.BackupHandle implementation; currently unset, to be added in a future PR.

We also add limiting fields to the GetBackupsRequest, to reduce the number of backup infos that have to be marshaled and sent over network; this is especially useful in the case where the caller is interested only in the most recent backup. In a future change we can revisit adding time-based filtering (i.e. "give me all backups before $x and after $y"), but I didn't want to tackle that now.

Finally, I updated the CLI to expose the limit field, and also to change the posargs from $keyspace $shard as two arguments to the more standard ${keyspace}/${shard} single argument.

Examples:

❯ vtctldclient --server ":15999" GetBackups commerce/0

❯ vtctldclient --server ":15999" GetBackups commerce/0 -j
{
  "backups": []
}
❯ vtctlclient -server ":15999" Backup zone1-101
❯ vtctldclient --server ":15999" GetBackups commerce/0
2021-06-12.185714.zone1-0000000101
❯ vtctlclient -server ":15999" Backup zone1-102
❯ vtctldclient --server ":15999" GetBackups commerce/0
2021-06-12.185714.zone1-0000000101
2021-06-12.185730.zone1-0000000102
❯ vtctldclient --server ":15999" GetBackups commerce/0 -l 1
2021-06-12.185730.zone1-0000000102
❯ vtctldclient --server ":15999" GetBackups commerce/0 -l 1 -j
{
  "backups": [
    {
      "name": "2021-06-12.185730.zone1-0000000102",
      "directory": "commerce/0",
      "keyspace": "commerce",
      "shard": "0",
      "tablet_alias": {
        "cell": "zone1",
        "uid": 102
      },
      "time": {
        "seconds": "1623524250",
        "nanoseconds": 0
      },
      "engine": "",
      "status": 0
    }
  ]
}

Related Issue(s)

#7352

Checklist

• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[doeg]

Looks good to me. Neither comment is blocking.

[doeg]

Non-blocking (scope-creepy) suggestion: colocating this backup name parse logic with the format call that happens in mysqlctl/backup.go could be useful for searchability (and any future refactors).

[doeg]

It might be useful to create + link an issue for this. Up to you!

[ajm188]

#8332