Backup provider improvements

### The required feature described as a wish

Currently, with the backup implementation, I found the following issues/limitations

**Issue 1**

**Allow multiple backup framework providers at zone level**

**Steps to reproduce the issue**

1. Have a CloudStack environment with One zone and multiple clusters ( KVM. VMware)

2. Configure VEEAM for vmare cluster

https://docs.cloudstack.apache.org/en/4.22.0.0/adminguide/veeam_plugin.html

3. Configure NAS for KVM cluster

https://docs.cloudstack.apache.org/en/4.22.0.0/adminguide/nas_plugin.html#nas-backup-and-recovery-plugin

4. Configure the Global setting "backup.framework.provider.plugin" = veeam.nas

5. Navigate to Service offering > Backup offering

```

2025-12-17 07:24:28,644 ERROR [c.c.a.AlertManagerImpl] (CapacityChecker:[ctx-96786e18]) (logid:0203c46c) Exception in CapacityChecker com.cloud.utils.exception.CloudRuntimeException: Failed to find backup provider by the name: veeam,nas
at org.apache.cloudstack.backup.BackupManagerImpl.getBackupProvider(BackupManagerImpl.java:1656)
at org.apache.cloudstack.backup.BackupManagerImpl.getBackupProvider(BackupManagerImpl.java:1648)
at org.apache.cloudstack.backup.BackupManagerImpl.getBackupStorageUsedStats(BackupManagerImpl.java:2262)
at org.apache.cloudstack.backup.BackupManagerImpl.getBackupStorageUsedStats(BackupManagerImpl.java:176)
at jdk.internal.reflect.GeneratedMethodAccessor417.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:569)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344)

```

**Current behaviour**

Currently, only one Backup framework is allowed per zone, it would be

**Expected behaviour**

It would be great if we could configure the "backup.framework.provider.plugin" at cluster level rather than zone level or support multiple backup providers at zone level

---------------
**Issue 2**

**Associate the backup offerings based on the hypervisor or cluster**

**Steps to reproduce the issue**

1. Have multiple backup offerings one for kvm and one for vmware

2. Navigate to deploy vm form Compute > Select a KVM host or KVM template , all the backup offering are displayed

Similarly, select a VMWare host or vmware template , all the backup offering are displayed

3. Similarly, in the instance view all the backup offerings are displayed

**Expected behaviour**

It would be great if we could display the backup offerings based on the hypervisor or cluster type ( KVM or vmware)

Beginnen Sie mit den in der Stacktrace gezeigten Stellen in BackupManagerImpl.java und lesen Sie die verlinkte Dokumentation zu den Veeam- und NAS-Plugins. Reproduzieren Sie die Zonenkonfiguration und untersuchen Sie die in diesem Issue beschriebenen Compute-Bereitstellungs- und Instanzansichten. Als abgeschlossen gilt die Aufgabe, wenn mehrere Provider wie erforderlich koexistieren können und Backup-Angebote nach Hypervisor- oder Clustertyp gefiltert werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.