log info when endpoints change for a balancer

[ElvinEfendi]

What this PR does / why we need it:
See #4023 (comment)

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

Special notes for your reviewer:

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@@            Coverage Diff            @@
##             master    #4120   +/-   ##
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  Coverage          ?   57.76%           
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  Files             ?       87           
  Lines             ?     6459           
  Branches          ?        0           
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  Hits              ?     3731           
  Misses            ?     2296           
  Partials          ?      432

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[aledbf]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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