chore: set update strategy for the azure-cnms addon

[jadarsie]

Reason for Change:
Our air-gap validations show that the azure-cni-networkmonitor pods running on control-plane nodes do not reach the Running state after an upgrade operation (AKSe v0.48+K8s v1.15 to v1.16). Switching updateStrategy.type to RollingUpdate (from default OnDelete) fixes the problem.

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
Should we update all addons updateStrategy?

[codecov]

Codecov Report

Merging #3571 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3571   +/-   ##
=======================================
  Coverage   73.19%   73.19%           
=======================================
  Files         147      147           
  Lines       25078    25078           
=======================================
  Hits        18355    18355           
  Misses       5589     5589           
  Partials     1134     1134           

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	54.08% <ø> (ø)

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jadarsie, mboersma

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