Allow enabling/disabling opentracing for ingresses

[willthames]

What this PR does / why we need it:

Occasionally you might want to enable opentracing only for a specific set of ingresses, or disable a specific ingress (this appears to be the easiest way to not trace specific paths such as an external healthcheck). While enabling opentracing is possible using location snippets, disabling opentracing is not currently possible (because opentracing_propagate_context cannot be unset once set).

Special notes for your reviewer:

I would have liked the default for enabled to be the value for enable-opentracing from the ConfigMap as that would have simplified a lot of logic (I wouldn't need the Set property and the nginx template would have been more readable). I couldn't work out how to do that, but if it's possible, I would definitely be happy to refactor this change.

[k8s-ci-robot]

Hi @willthames. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[aledbf]

/ok-to-test

[codecov-io]

Codecov Report

Merging #4732 into master will decrease coverage by <.01%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master    #4732      +/-   ##
==========================================
- Coverage   58.62%   58.61%   -0.01%     
==========================================
  Files          88       89       +1     
  Lines        6743     6761      +18     
==========================================
+ Hits         3953     3963      +10     
- Misses       2353     2361       +8     
  Partials      437      437

Impacted Files	Coverage Δ
internal/ingress/types.go	0% <ø> (ø)	⬆️
internal/ingress/controller/controller.go	50.55% <100%> (+0.12%)	⬆️
internal/ingress/annotations/annotations.go	81.94% <100%> (+0.25%)	⬆️
internal/ingress/annotations/opentracing/main.go	53.84% <53.84%> (ø)
internal/ingress/controller/store/backend_ssl.go	42.85% <0%> (-0.45%)	⬇️
internal/ingress/controller/store/store.go	58.51% <0%> (-0.13%)	⬇️

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[aledbf]

@willthames please check the gofmt error

!!! 'gofmt -s' needs to be run on the following files: 
./internal/ingress/annotations/opentracing/main.go

[willthames]

@aledbf that's done now, thanks!

[aledbf]

/lgtm

[aledbf]

@willthames thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [aledbf]

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[Stono]

This is a great feature - thanks for adding it :-)
However we found a bug where the annotation doesn't seem to apply without a restart of the nginx controller (see #4933)