Use etcd-snapshot-retention as default for s3 if etcd-s3-retention is not set

[brandond]

Proposed Changes

Use etcd-snapshot-retention as default for s3 if etcd-s3-retention is not set

Types of Changes

enhancement

Verification

See linked issue

Testing

Linked Issues

• S3 snapshot retention may not store as may snapshots as expected after upgrading to 2025-08 releases #13769

User-Facing Change

Further Comments

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 22.35%. Comparing base (3f5eec4) to head (5c960ed).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/cli/etcdsnapshot/etcd_snapshot.go	0.00%	2 Missing ⚠️
pkg/cli/server/server.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13770   +/-   ##
=======================================
  Coverage   22.35%   22.35%           
=======================================
  Files         193      193           
  Lines       15606    15613    +7     
=======================================
+ Hits         3488     3490    +2     
- Misses      11639    11644    +5     
  Partials      479      479           

Flag	Coverage Δ
unittests	22.35% <20.00%> (+<0.01%)	⬆️

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