feat: add configmap support

[phanipadala]

• Add function to validation configmap exists in desired namespace.
• Add unit tests

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 46.45%. Comparing base (5b5a76b) to head (b807b2c).

❗ Current head b807b2c differs from pull request most recent head a7f9028

Please upload reports for the commit a7f9028 to get more accurate results.

Files	Patch %	Lines
kubedog.go	0.00%	2 Missing ⚠️
pkg/kube/kube.go	0.00%	2 Missing ⚠️
pkg/kube/structured/structured_helper.go	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #156      +/-   ##
==========================================
+ Coverage   45.80%   46.45%   +0.65%     
==========================================
  Files          19       19              
  Lines        1871     1890      +19     
==========================================
+ Hits          857      878      +21     
+ Misses        900      896       -4     
- Partials      114      116       +2     

Flag	Coverage Δ
unittests	46.45% <70.00%> (+0.65%)	⬆️

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[garomonegro]

LGTM