Warn when HelmRelease values are the wrong type

[squaremo]

When interpreting the spec.values part of a HelmRelease, fluxd will silently skip any images with a tag that isn't typed string. That's because they really should be strings, since e.g., 1.10 in YAML will end up as 1.1 if not quoted.

This is surprising if you have not internalised that quirk of YAML, so we should put a warning in the log that the .spec.values is faulty, in those cases.

[kingdonb]

No further enhancements can land in Flux v1,

• Flux v1 is in maintenance mode #3320

Arguably this is a bug, (but not one I think we are likely to fix in Flux v1.)

If there was an implementation presented, I would still consider it for merge.