WAL arhives uploaded always, ignoring isWALArchiver setting

If user will omit or configure `isWALArchiver=false` inside cluster CR - barman-cloud plugin will still upload WAL to S3.

Steps done:
Tried omitting `isWALArchiver`:
```
plugins:
- name: barman-cloud.cloudnative-pg.io
enabled: true
parameters:
barmanObjectName: cnpg-cluster-01-backup
```
and setting it to `false`:

```
plugins:
- name: barman-cloud.cloudnative-pg.io
enabled: true
isWALArchiver: false
parameters:
barmanObjectName: cnpg-cluster-01-backup
```
Expected result: no `wal` folder would be created
Actual result: cnpg-cluster-01-backup S3 object get `wal` folder and files inside after cluster creation

首先，追踪 barman-cloud plugin 在 cluster CR 的 isWALArchiver 设置被省略或为 false 时如何处理该设置。使用所示配置复现报告中的 cluster 创建，并检查 S3 对象中是否出现 wal 文件夹和文件。完成的标准是：两种情况下 WAL 上传都被禁用，并且在以其他方式配置时仍保持启用。

由索引模型根据 Issue 内容生成。