This commit changes the state package so that errors encountered while
expanding templates for custom labels and annotations are returned
from the function. This is not used at present, but will be used in the
future as we look at how to offer better feedback to users who don't
have access to logs, for example our customers who use Hosted Grafana.
This commit changes how labels are printed in templates for custom
annotations and labels from map[foo:bar bar:baz] to foo=bar, bar=baz.
Labels are comma separated, and sorted in increasing order.
This commit moves templating from the state package to a sub-package
called template. This sub-package will be the logical package for
future ease-of-use improvements to templating custom annotations
and labels.
