Add custom labels option to application configs

[naorlivne]

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Expected/Wanted Behavior

It should be possible to add custom labels on an app level to running containers in addition to the existing Nebula labels of:

• "app_name"
• "orchestrator"

The existing Nebula labels should not be possible to be overwritten as so there should be some failsafe check to prevent overwriting them.

This should be an optional dict in the app config which defaults to {} if not set and in which case only the existing Nebula labels should be added.

Actual Behavior

Currently only the default labels are added to running containers.