cli: 'repo sync-to' will compare only unique ID not the entire format

[jkowalski]

This allows it to tolerate format changes, such as the ones made
during upgrade.

Fixes #1421

[codecov]

Codecov Report

Merging #1423 (fd3d204) into master (d5c619f) will increase coverage by 0.11%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master    #1423      +/-   ##
==========================================
+ Coverage   68.26%   68.38%   +0.11%     
==========================================
  Files         366      366              
  Lines       28845    28884      +39     
==========================================
+ Hits        19691    19751      +60     
+ Misses       7503     7487      -16     
+ Partials     1651     1646       -5     

Impacted Files	Coverage Δ
cli/command_repository_sync.go	70.18% <42.85%> (-0.02%)	⬇️
cli/command_content_verify.go	73.68% <0.00%> (-5.27%)	⬇️
internal/epoch/epoch_manager.go	84.71% <0.00%> (+0.05%)	⬆️
repo/blob/sharded/sharded.go	86.70% <0.00%> (+1.89%)	⬆️
repo/blob/filesystem/filesystem_storage.go	66.31% <0.00%> (+2.13%)	⬆️
repo/content/content_manager_iterate.go	91.71% <0.00%> (+2.20%)	⬆️
internal/server/source_manager.go	73.24% <0.00%> (+3.27%)	⬆️
snapshot/snapshotfs/estimate.go	100.00% <0.00%> (+3.33%)	⬆️
internal/cache/persistent_lru_cache.go	82.27% <0.00%> (+3.79%)	⬆️
... and 1 more

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