Allow configuration of renovate config.json using yaml

[ericwyles]

Currently in the config chart we have renovate.config that expects a block of json that gets fed as a secret to renovate for the base config. This isn't super convenient to work with but currently we also don't use a big block of json here so it's working ok.

We should investigate if we can provide a yaml format for this and convert that to json for more complex configurations in case that is easier to work with than maintaining a block of json inside the values.yaml.