cleanup: unexport kubernetes.Client method

[imjasonh]

Signed-off-by: Jason Hall [email protected]

The method is only used inside the package, and we shouldn't recommend folks depend on it, so let's unexport it.

The method encapsulates trying to create a k8s client from local environment config, and if one can't be found, it falls back to creating an in-cluster k8s client. This is used by both the policy controller, which uses the in-cluster config, and cosign generate-key-pair k8s://ns/secret-name, which may use a regular user config, or if run in a K8s cluster, would use the in-cluster config. As the policy controller moves out to its own repo we might want to consider just having it assume the in-cluster config.

This change also collapses three methods into one, for simplicity.

Release Note

NONE

[codecov-commenter]

Codecov Report

Merging #1973 (93f6a28) into main (3ddce4c) will decrease coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1973      +/-   ##
==========================================
- Coverage   34.80%   34.70%   -0.10%     
==========================================
  Files         153      152       -1     
  Lines       10119    10078      -41     
==========================================
- Hits         3522     3498      -24     
+ Misses       6226     6210      -16     
+ Partials      371      370       -1     

Impacted Files	Coverage Δ
pkg/cosign/kubernetes/client.go	0.00% <0.00%> (ø)
pkg/cosign/kubernetes/secret.go	37.34% <0.00%> (ø)
pkg/cosign/tuf/client.go	64.07% <0.00%> (-0.65%)	⬇️
cmd/cosign/cli/options/predicate.go	0.00% <0.00%> (ø)
pkg/cosign/tuf/store.go

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