Change usage examples to use JSON config instead of YAML

[brendan-kellam]

Currently, it's a bit confusing that all of the examples of the helm chart have the Sourcebot configuration in YAML, while all of the main docs are in JSON: https://docs.sourcebot.dev/docs/connections/overview

We should updat e the docs to instruct folks to create a seperate config.json file, and then reference that inside of the helm values.yaml.