BP-1255: Delay use of Redis to after startup

The Statistics module of the Fleet Manager needs to load data from Redis. Previously, it was relying on a connection started during the import of some Python modules, but that was changed in BP-944.

This commit changes the code to only load data from Redis when the API is first called, rather than during Python import, so that we can be sure the connection to Redis is already established.

Ticket: BP-1255

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MOV-AI / backend

BP-1255: Delay use of Redis to after startup #208

Quality Gate passed