Docs: configmap: use-gzip

[ellieayla]

What this PR does / why we need it:

https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#use-gzip doesn’t say that the default of “use-gzip” is “true”, and instead lists the default of the “gzip-types” field.

Move the gzip-types value default from the use-gzip to the gzip-types heading, and link to it from the copy around use-gzip

Document that the use-gzip default is true, matching the style of other configmap items.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

No issue

Special notes for your reviewer:

https://kubernetes.slack.com/archives/CANQGM8BA/p1557933421497900

[aledbf]

/lgtm
/approve

[aledbf]

@alanjcastonguay thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[codecov-io]

Codecov Report

Merging #4089 into master will decrease coverage by 0.31%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4089      +/-   ##
==========================================
- Coverage   57.78%   57.46%   -0.32%     
==========================================
  Files          87       87              
  Lines        6438     6475      +37     
==========================================
+ Hits         3720     3721       +1     
- Misses       2288     2323      +35     
- Partials      430      431       +1

Impacted Files	Coverage Δ
internal/ingress/zz_generated.deepcopy.go	0% <0%> (ø)	⬆️
internal/watch/file_watcher.go	84.61% <0%> (+3.84%)	⬆️

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