Fix snapshot prune

[brandond]

Proposed Changes

• Fix k3s etcd-snapshot prune with nonexistent etc-snapshot-dir
• Fix k3s etcd-snapshot prune not loading snapshot-retention from config file

Types of Changes

bugfix

Verification

See linked issues

Testing

Linked Issues

• Panic when etcd-snapshot-dir does not exist #9316 (comment)
• etcd-snapshot prune does not load retention policy from config #9532

User-Facing Change

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 35.00000% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 42.91%. Comparing base (de82584) to head (c0f3036).
Report is 11 commits behind head on master.

Files	Patch %	Lines
pkg/etcd/snapshot.go	31.57%	10 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9502      +/-   ##
==========================================
- Coverage   49.42%   42.91%   -6.51%     
==========================================
  Files         151      154       +3     
  Lines       13475    13522      +47     
==========================================
- Hits         6660     5803     -857     
- Misses       5474     6551    +1077     
+ Partials     1341     1168     -173     

Flag	Coverage Δ
e2etests	?
inttests	39.48% <35.00%> (+0.02%)	⬆️
unittests	15.96% <0.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.