fix: supports specifing incmental backup in release-0.9

[gnolong]

fix #8789
ref #8788

[codecov]

Codecov Report

Attention: Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.

Project coverage is 64.45%. Comparing base (87abc8a) to head (27024dc).
Report is 1 commits behind head on release-0.9.

Files with missing lines	Patch %	Lines
...trollers/apps/transformer_cluster_backup_policy.go	18.18%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release-0.9    #8790      +/-   ##
===============================================
- Coverage        64.59%   64.45%   -0.15%     
===============================================
  Files              359      359              
  Lines            46306    46317      +11     
===============================================
- Hits             29913    29852      -61     
- Misses           13718    13784      +66     
- Partials          2675     2681       +6     

Flag	Coverage Δ
unittests	64.45% <18.18%> (-0.15%)	⬇️

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