fix: start only one instance of ChartManagementService scheduled job

What does this PR do? (Please give us a brief description of what this PR does.)

This PR fixes a bug where ChartManagementService.start() is called multiple times. This will create multiple instances of the background task, which results in duplicated database calls when the task runs every 20 minutes. I've tested this on my own instance and everything seems to work correctly.

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