Add changelog for v1.15.3

[mboersma]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

Adds a changelog file for the impending CAPZ v1.15.3 patch release.

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.18%. Comparing base (1e9f0d9) to head (bf9aeb9).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4988   +/-   ##
=======================================
  Coverage   51.17%   51.18%           
=======================================
  Files         274      274           
  Lines       24625    24625           
=======================================
+ Hits        12603    12605    +2     
+ Misses      11236    11234    -2     
  Partials      786      786           

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[Jont828]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: b7c3b23da13b68d1022db2e9547f9d42cb98a485

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Jont828

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