Add "k3s certificate check" clause for better test coverage

[dereknola]

Proposed Changes

• Adds coverage of the k3s certificate check CLI in testing.
• Adds "--output table" format for cert check

derek@degion:~/rancher/k3s$ sudo ./dist/artifacts/k3s certificate check -o table
INFO[0000] Acquiring lock file /var/lib/rancher/k3s/data/.lock 
INFO[0000] Preparing data dir /var/lib/rancher/k3s/data/028414f76580c17e66747d4743a4ad51a705efcdc49cb61e619bdfb975acdb01 
INFO[0000] Server detected, checking agent and server certificates 

CERTIFICATE                      SUBJECT                                    STATUS  EXPIRES
-----------                      -------                                    ------  -------
client-admin.crt                 CN=system:admin,O=system:masters           OK      2025-12-20T19:55:36Z
client-admin.crt                 CN=k3s-client-ca@1734724536                OK      2034-12-18T19:55:36Z
client-kube-proxy.crt            CN=system:kube-proxy                       OK      2025-12-20T19:55:36Z
client-kube-proxy.crt            CN=k3s-client-ca@1734724536                OK      2034-12-18T19:55:36Z

Types of Changes

Testing

Verification

Coverage report

github.com/k3s-io/k3s/pkg/cli/cert/cert.go:52:			Check			66.7%

Testing

Linked Issues

#11484

User-Facing Change

Can now get a table output for `k3s certificate check` using `--output table` flag

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 32.69231% with 35 lines in your changes missing coverage. Please review.

Project coverage is 38.85%. Comparing base (bb32254) to head (467498f).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/cli/cert/cert.go	25.53%	31 Missing and 4 partials ⚠️

❗ There is a different number of reports uploaded between BASE (bb32254) and HEAD (467498f). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (bb32254)	HEAD (467498f)
unittests	2	0
e2etests	7	6

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11485      +/-   ##
==========================================
- Coverage   47.87%   38.85%   -9.03%     
==========================================
  Files         181      164      -17     
  Lines       18794    18238     -556     
==========================================
- Hits         8998     7086    -1912     
- Misses       8448     9948    +1500     
+ Partials     1348     1204     -144     

Flag	Coverage Δ
e2etests	35.23% <9.61%> (-7.81%)	⬇️
inttests	18.88% <32.69%> (-15.97%)	⬇️
unittests	?

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.

[brandond]

ohh a tabwriter, fancy