[Feature]: verify barmanObjectName

when referencing an `barmanObjectName ` in `externalCluster` that is used for recovery
and that does not exist
the creation of the cluster stops without error after "creating cluster role" phase

Therefor it would be good to verify the if the barmanObjectName exists

```
...
bootstrap:
#########################
# restore just in case...
#########################

recovery:
source: source
# recoveryTarget:
# targetTime: "2023-06-19 17:15:00.00000+02"

externalClusters:
- name: source
plugin:
name: barman-cloud.cloudnative-pg.io
parameters:
# Recovery Object Store (pull, read-only)
barmanObjectName: minio-store
serverName: xxx
...
```

跟踪 externalCluster 插件配置和 barmanObjectName 参数的 trace 恢复处理；issue 中未指定文件或测试。确定在创建集群期间引用的对象在哪里解析，然后验证缺少对象时会产生明确错误，而不是在 "creating cluster role" 阶段之后停止。

由索引模型根据 Issue 内容生成。