feat: [FFM-12441]: Make inventory repo backwards compatible with older config after #404

[jcox250]

What

• Before PR feat: [FFM-12441]: Optimise SSE events #404, inventory configs were stored as map[string]string. After PR feat: [FFM-12441]: Optimise SSE events #404, they use map[string]int64 for SSE optimizations. This PR lets us convert the old config format on startup to the new config format.

Why

• Without this change, if you ran a Proxy version <= 2.0.12, and then ran the release candidate version 2.0.13-rc.1 against a redis instance populated by a <= 2.0.12 of the Proxy. The 2.0.13-rc.1 version would error reading the old config from redis because the formats didn't match.

Testing

• Ran 2.0.12, saw the old format populated in redis
• Ran 2.0.13-rc.1, saw the error loading the load config
• Ran a build from this branch, there is no error loading config and it's converted to the new format and stored in redis