[LP#1940328] openstack-integrator 1.29 release adjustments for installation and upgrade

[addyess]

LP#1940328

Upgrade release documentation to include instructions on migrating from loadbalancer relation to the lb-consumers relation.

• reference updated overlays https://github.com/charmed-kubernetes/bundle/pull/889
• reference updated charmhub docs

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[evilnick]

thanks @mateoflorido Have reviewed the text and made a few changes. @addyess if you want to address Mateo's comments I will approve and merge