Update core modules to v1.19 and Go to v1.15

[maciaszczykm]

• Bumps k8s to v1.19.0
• Bumps Go to v.1.15.1 (requirement set to 1.15)
• Bumps golangci-lint to v1.30.0

[k8s-ci-robot]

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This pull-request has been approved by: maciaszczykm

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[codecov]

Codecov Report

Merging #5497 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5497      +/-   ##
==========================================
+ Coverage   45.21%   45.26%   +0.04%     
==========================================
  Files         214      214              
  Lines       10261    10261              
  Branches      111      111              
==========================================
+ Hits         4640     4645       +5     
+ Misses       5350     5345       -5     
  Partials      271      271              

Impacted Files	Coverage Δ
src/app/frontend/login/component.ts	82.50% <0.00%> (+1.25%)	⬆️
...p/backend/integration/metric/common/aggregation.go	90.90% <0.00%> (+1.81%)	⬆️
src/app/backend/sync/secret.go	73.26% <0.00%> (+2.97%)	⬆️

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