Remove silent error when client-key/client-certificate is malformed

[goenning]

Motivation

malformed client-key/client-certificate are currently being ignored

Solution

bubble up the error instead of silently ignoring it

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.5%. Comparing base (e7060a8) to head (c0e456a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
kube-client/src/config/file_config.rs	79.0%	4 Missing ⚠️
kube-client/src/client/config_ext.rs	66.7%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1966     +/-   ##
=======================================
- Coverage   76.5%   76.5%   -0.0%     
=======================================
  Files         89      89             
  Lines       8585    8596     +11     
=======================================
+ Hits        6565    6569      +4     
- Misses      2020    2027      +7     

Files with missing lines	Coverage Δ
kube-client/src/config/mod.rs	54.7% <100.0%> (ø)
kube-client/src/client/config_ext.rs	52.5% <66.7%> (-0.1%)	⬇️
kube-client/src/config/file_config.rs	78.5% <79.0%> (-0.9%)	⬇️

... and 3 files with indirect coverage changes

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[clux]

Thanks for this. Sorry, just getting around to things again.

One minor request if you have time for it, otherwise this looks sensible to me.

[clux]

a test for an error case here might be useful, since this is a bit difficult to fully trust in your head