fix: warning added to NOTES about installationType

[jessesimpson36]

Which problem does the PR fix?

Related to #2286

global.multiregion.installationType is going away, so if anyone uses this option, they should get a notice that says:

[camunda][warning]
DEPRECATION NOTICE: Starting from appVersion 8.7, the Camunda Helm chart will no longer support the global.multiregion.installationType option. This is replaced with a new procudure for managing multi-region installations documented here:
https://docs.camunda.io/docs/self-managed/operational-guides/multi-region/dual-region-operational-procedure/
Please unset this option to remove the warning.

What's in this PR?

if the option is set, print the warning.

Checklist

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