This commit changes extractEvalString to sort NumberCaptureValues
in ascending order of Var before building the output string. This
means that users will see EvaluationString in a consistent order,
but also make it possible to assert its output in tests.
* Expand the value of math and reduce expressions in annotations and labels
This commit makes it possible to use the values of reduce and math
expressions in annotations and labels via their RefIDs. It uses the
Stringer interface to ensure that "{{ $values.A }}" still prints the
value in decimal format while also making the labels for each RefID
available with "{{ $values.A.Labels }}" and the float64 value with
"{{ $values.A.Value }}"
When, and currently only when using a classic condition, evaluation information is added (which is like the EvalMatches from dashboard alerting).
This is returned via the API and can be included in notifications by reading the `__value__` label attached `.Alerts` in the template. It is a string.
