[TASK] Make use of the `gatewayAddress` property instead of the deprecated `brokerContactPoint` in Operate

[romansmirnov]

Related to:

With https://github.com/camunda/zeebe/issues/17062, Operate is distributed together with Zeebe as a Single JAR (Distribution). By that, the Operate configuration is part of the application.yaml file and no longer in application.yml (without an a in yaml). Additionally, a while ago the configuration property brokerContactPoint was marked as deprecated, and instead the property gatewayAddress must be used.

All that together, it may cause Operate to try to connect to Zeebe via localhost:26500, which is caused by the order Spring loads/applies the application.yml and application.yaml files. Plus, how Operate sets the gatewayAddress (even when using the brokerContactPoint), see https://github.com/camunda/zeebe/pull/17571

While this will be fixed in Operate itself, I suggest adjusting the config map accordingly to reflect the changes in the Helm Charts as well.

Overview:

• [ ] In Operate, use gatewayAddress instead of brokerContactPoint
• [ ] In Operate, change application.yml to application.yaml to be mounted

Actions:

• This change must be released with 8.6.0.

[romansmirnov]

Opened a PR to apply the changes: https://github.com/camunda/camunda-platform-helm/pull/1647