Align etcd-snapshot-dir default path description

[majabojarska]

Proposed Changes

The CLI documentation (i.e. --help output) should be a reliable source of truth for the end user. This PR ensures that the default etcd snapshot location matches the expectations that are being set by the CLI. It updates the --etcd-snapshot-dir option's description to match the effective default snapshot path (one that will be used by the server).

Types of Changes

Bugfix, a simple update to the --etcd-snapshot-dir option descriptions for the server and etcd-snapshot commands.

Verification

This section is mostly based on the reproduction steps from #11570

1. Run k3s server --help | grep '\-dir'.
2. Ensure the reported default value for --etcd-snapshot-dir matches ${data-dir}/server/db/snapshots. That's been confirmed to be the actual path in the issue's analysis.
3. Run k3s etcd-snapshot --help | grep '\-dir'.
4. Repeat step 2.

Testing

Test coverage updates are not applicable to this PR, since it introduces no changes to the logic.

Linked Issues

#11570

User-Facing Change

Align the CLI-reported default `--etcd-snapshot-dir` value with the actual one (`server`, `etcd-snapshot` commands).

Further Comments

No further comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.80%. Comparing base (6b0247f) to head (8f2db0f).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11571      +/-   ##
==========================================
- Coverage   50.01%   47.80%   -2.22%     
==========================================
  Files         185      185              
  Lines       19265    19265              
==========================================
- Hits         9635     9209     -426     
- Misses       8236     8727     +491     
+ Partials     1394     1329      -65     

Flag	Coverage Δ
e2etests	40.59% <ø> (-3.70%)	⬇️
inttests	35.11% <ø> (-0.03%)	⬇️
unittests	17.03% <ø> (ø)

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