[grafana] Rate over 2 minutes since default Prometheus interval is 1m

[Miouge1]

What this PR does / why we need it:

Prometheus' default scrape_interval is 1m, see prometheus doc, making irate(mymetrics{}[1m]) not return any data with the default scrape_interval.

In order to make this Grafana dashboard as easy to use as possible I think it should work out of the box with the Prometheus defaults, therefore I suggest to switch 1m for 2m but other values could also be useful.

Special notes for your reviewer:
Example: prometheus/prometheus#3194

[aledbf]

@discordianfish WDYT about this?

[discordianfish]

2m might be a better default, that's right. Even better though would be using $__interval and rate() instead of irate(). This has it's own problems though: grafana/grafana#11451

[Miouge1]

I resolved the conflicts in the latest commit. I would suggest to move forward with this and see how the discussion with $__interval evolves.

[codecov-io]

Codecov Report

Merging #2884 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2884      +/-   ##
==========================================
- Coverage   47.58%   47.54%   -0.04%     
==========================================
  Files          77       76       -1     
  Lines        5634     5483     -151     
==========================================
- Hits         2681     2607      -74     
+ Misses       2600     2542      -58     
+ Partials      353      334      -19

Impacted Files	Coverage Δ
internal/ingress/controller/nginx.go	11.28% <0%> (-4.76%)	⬇️
internal/watch/file_watcher.go	80.76% <0%> (-3.85%)	⬇️
internal/net/net.go	72.72% <0%> (-2.28%)	⬇️
internal/ingress/annotations/annotations.go	80.64% <0%> (-0.31%)	⬇️
internal/ingress/controller/store/store.go	62.68% <0%> (-0.11%)	⬇️
internal/ingress/controller/config/config.go	98.26% <0%> (-0.05%)	⬇️
internal/ingress/sslcert.go	50% <0%> (ø)	⬆️
...ternal/ingress/annotations/backendprotocol/main.go
internal/ingress/controller/controller.go	2.22% <0%> (+0.02%)	⬆️
internal/ingress/types_equals.go	13.17% <0%> (+0.08%)	⬆️
... and 5 more

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[aledbf]

/lgtm
/approve

[aledbf]

@Miouge1 thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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