Issue 7211: support concatenate objects

[Lyndon-Li]

Fix issue #7211. Enable advanced feature capability and add support to concatenate objects for unified repo.

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (3b8370e) 61.64% compared to head (24c4eb0) 61.65%.
Report is 11 commits behind head on main.

Files	Patch %	Lines
pkg/uploader/provider/kopia.go	0.00%	4 Missing and 1 partial ⚠️
pkg/repository/udmrepo/kopialib/lib_repo.go	82.60%	4 Missing ⚠️
pkg/uploader/kopia/snapshot.go	0.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7452   +/-   ##
=======================================
  Coverage   61.64%   61.65%           
=======================================
  Files         262      262           
  Lines       28477    28522   +45     
=======================================
+ Hits        17556    17586   +30     
- Misses       9689     9701   +12     
- Partials     1232     1235    +3     

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