Add Telemetry Permissions Configuration

Context:

Users will have the ability to opt in and out of sending Optimize data to telemetry. The initial setting should be stored in the config as `initializeTelemetry`. After starting Optimize, telemetry can be turned off/on via a rest api - we need to store whether telemetry has been enabled/disabled via api as well.

For the first iteration, there will be just one telemetry flag that decides if Optimize can send essential data to telemetry. For future iterations, there may be more granular permissions (e.g. permissions to send specific data only).
Whether or not this config setting can be adjusted in the UI is still to be decided, so there's no frontend part of this yet.

Note:

In the future, we may add flags to enable/disable things like errorReports/update notifications etc which could potentially be stored in the same index as the telemetry permissions, so it would be nice to add some sort of generic index that we can extend later (rather than a specific telemetry permissions index)

AT:

• an `initializeTelemetry` telemetry permissions flag is added to the config, default value false (naming consistent with engine config)
• a telemetryEnabled setting is stored that reflects whether or not telemetry is currently enabled
• api endpoints are added to write and retrieve settings
• the new api endpoints are documented on confluence (https://confluence.camunda.com/display/CO/Settings)
• only superusers are allowed to configure settings