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