docs: Update 2.3 notes - mention helm chart

[asfaltboy]

Spent some time looking this up, as we use the helm chart. I believe values should be copied as-is into the notifications section of the argo-cd chart. Please correct me if I'm wrong in this assumption

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[codecov]

Codecov Report

Merging #9512 (1ef049c) into master (7faae31) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9512   +/-   ##
=======================================
  Coverage   45.75%   45.75%           
=======================================
  Files         221      221           
  Lines       26293    26293           
=======================================
  Hits        12031    12031           
  Misses      12606    12606           
  Partials     1656     1656           

Impacted Files	Coverage Δ
util/settings/settings.go	48.16% <0.00%> (ø)

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[jannfis]

LGTM. Thanks for improving the docs, @asfaltboy !