Add basic security context to deployment YAMLs

[praseodym]

What this PR does / why we need it: Adding a security context with runAsNonRoot: false to the pod template indicates the pod's intention to run as root, and will let Kubernetes decide upon the correct pod security policy.

Which issue this PR fixes: fixes #2400

[praseodym]

/assign @antoineco

[codecov-io]

Codecov Report

Merging #2447 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2447      +/-   ##
==========================================
+ Coverage   41.61%   41.67%   +0.05%     
==========================================
  Files          74       74              
  Lines        5291     5291              
==========================================
+ Hits         2202     2205       +3     
+ Misses       2792     2790       -2     
+ Partials      297      296       -1

Impacted Files	Coverage Δ
cmd/nginx/main.go	23.44% <0%> (+2.06%)	⬆️

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[antoineco]

/lgtm

[praseodym]

/assign @caseydavenport

[aledbf]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, antoineco, praseodym

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