Add vts-sum-key config flag

[nicknovitski]

Currently, vts metrics use the server zone key * to indicate "all other server zones combined." The prometheus exporter translates this into a label with the same value. I use a datadog agent to read the prometheus metrics, which turns the label into a "tag", but strips out characters which the datadog service cannot accept, including *. This means the label value * becomes an empty string tag value.

So for example the prometheus metric nginx_requests_total{ingress_class="nginx",namespace="",server_zone="*"} is turned into a datadog metric named nginx.requests_total, with the tags ingress_class:nginx, namespace:, and server_zone:.

This isn't so bad, except the same thing happens to metrics for the server zone which includes (I believe) the default backend and metrics server, labeled server_zone="_". So I have different metrics numbers with the same tags, getting sent to datadog all the time, which makes monitoring seemingly impossible.

The workaround I've done is to create a custom nginx.conf template exactly like the normal one, except with one additional line: vhost_traffic_status_display_sum_key total; And maybe someday I'll just use prometheus instead of datadog. But in the meantime, I thought this would be a nice feature to have.

[codecov-io]

Codecov Report

Merging #2356 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2356      +/-   ##
==========================================
+ Coverage   39.11%   39.12%   +0.01%     
==========================================
  Files          73       73              
  Lines        5203     5204       +1     
==========================================
+ Hits         2035     2036       +1     
  Misses       2878     2878              
  Partials      290      290

Impacted Files	Coverage Δ
internal/file/bindata.go	57.42% <ø> (ø)	⬆️
internal/ingress/controller/config/config.go	98.21% <100%> (+0.01%)	⬆️

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[nicknovitski]

Okay, I'll give it a try: /assign @dcbw

[nicknovitski]

Updated to resolve bindata conflict.

[gianrubio]

/lgtm

[aledbf]

/lgtm

[aledbf]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[aledbf]

@gianrubio thanks for the review.