Fix secretsencrypt race conditions

[brandond]

Proposed Changes

Fix multiple race conditions in k3s startup that could cause handled and unhandled panics

Types of Changes

bugfix

Verification

See linked issues

Testing

todo: #11647

Linked Issues

• Secret encryption rotation panics if status checked during k3s startup #12339
• rke2-server panics when restarting after secrets-encrypt prepare on split etcd/controlplane setup rancher/rke2#8236

User-Facing Change

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 19.89%. Comparing base (effe6ce) to head (cb68f5b).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/server/handlers/secrets-encrypt.go	0.00%	4 Missing ⚠️
pkg/cli/server/server.go	0.00%	3 Missing ⚠️
pkg/server/server.go	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (effe6ce) and HEAD (cb68f5b). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (effe6ce)	HEAD (cb68f5b)
e2etests	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #12351       +/-   ##
===========================================
- Coverage   41.07%   19.89%   -21.18%     
===========================================
  Files         166      184       +18     
  Lines       19000    19221      +221     
===========================================
- Hits         7804     3824     -3980     
- Misses      10003    14966     +4963     
+ Partials     1193      431      -762     

Flag	Coverage Δ
e2etests	?
unittests	19.89% <0.00%> (-0.19%)	⬇️

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