errcode: introduce error code management

[shashankram]

Introduces a pkg to manage error codes. Documentation
and tooling to inspect errors will be built around
the error code and description mapping provided by
this pkg.

Sample error log with error code:

{"level":"error","component":"errcode","error":"some error","error_code":"E1000","time":"2021-06-30T12:52:14-07:00","file":"errcode_test.go:14","message":"some error was seen"}

Part of #2866

Signed-off-by: Shashank Ram shashr2204@gmail.com

Description:

Affected area:

Functional Area
New Functionality	[X]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project? no

   • Did you notify the maintainers and provide attribution?

2. Is this a breaking change? no

[codecov-commenter]

Codecov Report

Merging #3706 (8bb7371) into main (0322387) will increase coverage by 0.02%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #3706      +/-   ##
==========================================
+ Coverage   67.65%   67.68%   +0.02%     
==========================================
  Files         181      182       +1     
  Lines        8772     8773       +1     
==========================================
+ Hits         5935     5938       +3     
+ Misses       2804     2802       -2     
  Partials       33       33              

Flag	Coverage Δ
unittests	67.68% <50.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/osm-controller/osm-controller.go	13.51% <0.00%> (ø)
pkg/errcode/errcode.go	100.00% <100.00%> (ø)
pkg/providers/kube/client.go	57.85% <0.00%> (+0.71%)	⬆️
...icate/providers/certmanager/certificate_manager.go	87.90% <0.00%> (+0.80%)	⬆️

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