feat: support filtering backup target pods by the alternative label selector

[gnolong]

fix #7072
Add fallbackLabelSelector field to podSelector in backuppolicy, and add fallbackRole field used to build fallbackLabelSelector in backuppolicytemplate. If backup controller fails to filter available target pods, it will use fallbackLabelSelector to filter target pods. This behavior only takes effect when strategy is set to Any in the podSelector, Any means backup controller only selects one available pod as the target.

For example, in a primary-secondary cluster, we have scheduled tasks to back up the secondary pod. In the past, If all secondary pods are unavailable, the backups would continuously fail. Now, with the fallbackLabelSelector used to filter backup target pod, if all secondary pods are unavailable, we can use it to select the primary pod for backups, to guarantee the continuity of scheduled backup tasks with a high probability.

[codecov]

Codecov Report

Attention: Patch coverage is 48.00000% with 39 lines in your changes missing coverage. Please review.

Project coverage is 64.84%. Comparing base (7149aaa) to head (ffd9d21).
Report is 53 commits behind head on main.

Files	Patch %	Lines
controllers/dataprotection/utils.go	65.11%	10 Missing and 5 partials ⚠️
...trollers/apps/transformer_cluster_backup_policy.go	35.00%	10 Missing and 3 partials ⚠️
pkg/dataprotection/utils/utils.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7831      +/-   ##
==========================================
- Coverage   64.90%   64.84%   -0.07%     
==========================================
  Files         345      345              
  Lines       42941    42967      +26     
==========================================
- Hits        27873    27864       -9     
- Misses      12632    12656      +24     
- Partials     2436     2447      +11     

Flag	Coverage Δ
unittests	64.84% <48.00%> (-0.07%)	⬇️

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[ldming]

Modify the PR title to describe the implemented functionality.

[gnolong]

Modify the PR title to describe the implemented functionality.

done

[wangyelei]

/cherry-pick release-0.9

[github-actions]

🤖 says: cherry pick action finished successfully 🎉!
See: https://github.com/apecloud/kubeblocks/actions/runs/10260853758