Allow empty Backup path  generate errors after update


### Summary
Performing major version upgrade from 13.8 to 14.4 using the UI, I didn't fill the backup path field, and the SGDbOps continue to use the old one, provoking the cluster to not start:

```
2023-01-23 09:50:11.200 UTC,,,8369,,63ce5853.20b1,3,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"listening on IPv4 address ""127.0.0.1"", port 5432",,,,,,,,,"","postmaster",,0
2023-01-23 09:50:11.206 UTC,,,8369,,63ce5853.20b1,4,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"listening on Unix socket ""/var/run/postgresql/.s.PGSQL.5432""",,,,,,,,,"","postmaster",,0
2023-01-23 09:50:11.217 UTC,,,8373,,63ce5853.20b5,1,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"database system was shut down in recovery at 2023-01-23 09:47:41 UTC",,,,,,,,,"","startup",,0
2023-01-23 09:50:11.416 UTC,,,8373,,63ce5853.20b5,2,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"restored log file ""00000002.history"" from archive",,,,,,,,,"","startup",,0
2023-01-23 09:50:11.627 UTC,,,8373,,63ce5853.20b5,3,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"restored log file ""00000003.history"" from archive",,,,,,,,,"","startup",,0
2023-01-23 09:50:11.873 UTC,,,8373,,63ce5853.20b5,4,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"entering standby mode",,,,,,,,,"","startup",,0
2023-01-23 09:50:12.086 UTC,,,8373,,63ce5853.20b5,5,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"restored log file ""00000003.history"" from archive",,,,,,,,,"","startup",,0
2023-01-23 09:50:12.095 UTC,,,8373,,63ce5853.20b5,6,,2023-01-23 09:50:11 UTC,,0,FATAL,XX000,"requested timeline 3 is not a child of this server's history","Latest checkpoint is at 2D7/EF00E0B0 on timeline 1, but in the history of the requested timeline, the server forked off from that timeline at 2D7/EB0093D0.",,,,,,,,"","startup",,0
2023-01-23 09:50:12.096 UTC,,,8369,,63ce5853.20b1,5,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"startup process (PID 8373) exited with exit code 1",,,,,,,,,"","postmaster",,0
2023-01-23 09:50:12.096 UTC,,,8369,,63ce5853.20b1,6,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"aborting startup due to startup process failure",,,,,,,,,"","postmaster",,0
2023-01-23 09:50:12.111 UTC,,,8369,,63ce5853.20b1,7,,2023-01-23 09:50:11 UTC,,0,LOG,00000,"database system is shut down",,,,,,,,,"","postmaster",,0

```


This is the the SGDbOps manifest generated:

```
apiVersion: stackgres.io/v1
kind: SGDbOps
metadata:
  annotations:
    stackgres.io/operatorVersion: 1.4.0
  creationTimestamp: "2023-01-23T09:35:50Z"
  generation: 5
  name: op2023-01-23-10-35-04
  namespace: my-db
  resourceVersion: "252313591"
  uid: ec77f0c9-7728-45f2-a70c-64efb01b51c8
spec:
  majorVersionUpgrade:
    backupPath: ""
    check: false
    clone: false
    link: true
    postgresVersion: "14.4"
    sgPostgresConfig: pgconfig-14
  maxRetries: 0
  op: majorVersionUpgrade
  scheduling:
    tolerations:
    - key: stackgres
      operator: Exists
  sgCluster: my-db
status:
  conditions:
  - lastTransitionTime: "2023-01-23T09:59:33Z"
    reason: OperationNotRunning
    status: "False"
    type: Running
  - lastTransitionTime: "2023-01-23T09:59:33Z"
    reason: OperationCompleted
    status: "True"
    type: Completed
  - lastTransitionTime: "2023-01-23T09:59:33Z"
    reason: OperationNotFailed
    status: "False"
    type: Failed
  majorVersionUpgrade:
    initialInstances:
    - my-db-0
    pendingToRestartInstances: []
    primaryInstance: my-db-0
    restartedInstances:
    - my-db-0
    sourcePostgresVersion: "13.8"
    targetPostgresVersion: "14.4"
  opRetries: 0
  opStarted: "2023-01-23T09:35:52Z"
```

#### Steps to reproduce

- Create an SGCluster with backup configuration and backup path set, for example: 

```
configurations:
    backups:
    - compression: lz4
      cronSchedule: 30 01 * * 6
      path: sgbackups.stackgres.io/my-db/my-db/13
```

- Create a Major version Upgrade SGDbOps without filling the backup path field (from the UI)
- The major version upgrade finished but the cluster will not start because of the value of the backup path

### Expected Behaviour

The Cluster is upgraded successfully and the sgbackups path is set with a new valid value.  

### Possible Solution

In the case to solve the issue I follow the next steps:

1. Delete the StackGres validation webhook (I did a backup first)
2. Edit the SGCluster and set the new value for the backup path
3. Re-create the validation webhook
4. Delete the sgcluster pod
5. wait for the cluster to start. 

It would be nice to have a warning message or error if you do not specify a correct value and prevent the SGDbOps to be created. 


### Environment

- StackGres version: 1.4.0
<!-- if you have used helm, you can use:  `helm get notes -n stackgres stackgres-operator` 
more generic: `kubectl get deployments -n stackgres stackgres-operator --template '{{ printf "%s\n" (index .spec.template.spec.containers 0).image }}'`
-->
- Kubernetes version: 1.23.14
<!--(use `kubectl version`) -->
- Cloud provider or hardware configuration: DigitalOcean


### Relevant logs and/or screenshots

<!-- (Paste any relevant logs - please use code blocks (```) to format console output,
logs, and code as it's very hard to read otherwise.) -->

Story points: 4.0