Instrument controller to show configReload metrics

[gianrubio]

This PR add prometheus metrics to detect when the controller fail to reload nginx configuration
Ex:

alert: IngressControllerFailedReload 
expr: ingress_controller_config_last_reload_successfull == 0
for: 10m

It also deprecate the reloadOperation metric because configReload does more than reloadOperation

[gianrubio]

/assign @aledbf

[aledbf]

@gianrubio please check the CI error

[codecov-io]

Codecov Report

Merging #2542 into master will decrease coverage by 0.05%.
The diff coverage is 12.5%.

@@            Coverage Diff             @@
##           master    #2542      +/-   ##
==========================================
- Coverage   40.74%   40.69%   -0.06%     
==========================================
  Files          73       73              
  Lines        5021     5033      +12     
==========================================
+ Hits         2046     2048       +2     
- Misses       2701     2711      +10     
  Partials      274      274

Impacted Files	Coverage Δ
internal/ingress/controller/controller.go	2.24% <0%> (-0.01%)	⬇️
internal/ingress/controller/metrics.go	27.27% <16.66%> (-6.07%)	⬇️

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[aledbf]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, gianrubio

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[aledbf]

@gianrubio thanks!