Fixed KUBERNETES_EXEC_INFO environment variable passed to auth plugins

[Razz4780]

Closes #1318

Motivation

Custom authentication plugin fails when used with this client. Authentication plugins expect KUBERNETES_EXEC_INFO environment variable, which should contain a serialized ExecCredential object. Field kind of this object should contain ExecCredential string.

Solution

Setting kind to ExecCredential before serialization.

[codecov]

Codecov Report

Merging #1320 (f6a6c69) into main (c3fbe25) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is 0.0%.

❗ Current head f6a6c69 differs from pull request most recent head 1872d6f. Consider uploading reports for the commit 1872d6f to get more accurate results

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1320   +/-   ##
=====================================
  Coverage   72.4%   72.4%           
=====================================
  Files         75      75           
  Lines       6343    6343           
=====================================
  Hits        4587    4587           
  Misses      1756    1756           

Files	Coverage Δ
kube-client/src/client/auth/mod.rs	50.5% <0.0%> (ø)

[clux]

oh, lol. yeah, lgtm 👍