Log warning in case of listDimensions returns empty list

[or-shachar]

Relates to #432 - print warning in case dimensions is empty.
Otherwise - it's hard to understand that configuration is wrong.

I wonder though if there is any scenario where the case of empty dimensions is actually okay.
If there are - then this warning may be spamming and wrong.

[matthiasr]

Hmm, good point. Googling around I found grafana/grafana#42798. Can we somehow distinguish between custom and AWS metrics?

[or-shachar]

Nice catch! I removed the warning from this case.

IIUC the only way for it to work for a metric with no dimension is if we add an empty List to the dimensions list, so at the end of this function, there must be at least one item in the returned list.

[or-shachar]

Also maybe we need to document that this configuration with empty list actually supports metric with no dimensions (and that no value implicates metric with no dimension)

[matthiasr]

Yes indeed, I think the documentation around dimensions could be less technical and more practical. Nonetheless, thank you for adding the warning!